Solve The Outbreak

Clue 1

Inside the concert hall where the music workshop was held.

The first reported case is a 37-year-old musician from Chicago named Zeke. You start by talking to Zeke to find out what he was doing before he got sick.

Zeke said that he started coughing and feeling very tired shortly after he led a music workshop for 50 students at a Chicago concert hall. He thought he might have picked something up from one of the students in the class, or perhaps he caught it 2 days ago on a flight home from vacation in Africa.

Tip

Zeke learned how to make djembes in Mali.

You decide to ask Zeke more about his trip to Africa.

You learn that Zeke and several of his friends took a trip to Mali last week. While they were there, Zeke took a side trip to meet a drum maker who taught him how to make djembes (African drums made of animal skins and wood). Zeke brought home 4 of the djembes he helped make.

Zeke and his friends returned home on the same 20-hour flight. After talking with Zeke's friends, you learn that he is the only one with a high fever, fatigue, cough, chest pain, and difficulty breathing.

Clue 2

The doctor suspects that the patients could be infected with anthrax.

More cases of the mysterious illness are being reported in Chicago and Milwaukee hospitals. Patients' loved ones are in a panic and are hoping you can help find out what's made everyone so sick.

Lab results show patients are infected with a bacterium that doctors suspect might be anthrax. You immediately send the samples to public health laboratories for testing, but that will take a couple of days.

In the meantime, you need to talk with everyone who is sick - and their families - to find out which activities they participated in before becoming sick. When you look at the responses to your questions, it seems that many of the sick people participated in the same activities recently - like working in a government building or attending a music event.

Data

Attack rates based on the interviews with the people who got sick and those who did not get sick ("controls").

You already have gotten information directly from sick patients or family members of those who died. You interview 85 people who are not sick, but participated in similar activities as those who are sick or died. In outbreak investigations we call these people the "population at risk of getting sick."

Each person was asked what they did in the 2 weeks before getting sick. The "attack rate" was calculated for each activity.

Hint: To find a possible source of the outbreak, look for both a high attack rate for those who participated in an activity and a low attack rate among those who did not participate.

Definition

Anthrax spores under high magnification.

Anthrax

Anthrax is a serious disease caused by a type of bacteria known as Bacillus anthracis. Anthrax is not contagious. You cannot catch it from another person, like you can catch the cold or flu.

Anthrax can be found naturally in the soil and can infect domestic and wild animals like cattle, sheep, and goats. The animals become sick when they eat spores (germs) in contaminated soil or vegetation.

People can get anthrax by:

• Handling products made from infected animals.
• Breathing in anthrax spores from animal products.
• Eating undercooked meat from infected animals.
• Being exposed to anthrax spores by bioterrorists.

Anthrax can get into the body through the skin, lungs, or digestive system.

Clue 3

Postal workers are watching for suspicious packages.

With the large number of government workers who are sick, you decide to look into it more. Police reports show that there was a bioterrorism threat 3 days before Zeke and the others got sick - a former government employee threatened to mail anthrax to his old office building in downtown Chicago.

You interview the 2 sick people from Milwaukee to find that neither of them had been in or around any government building in Chicago in the 2 weeks before getting sick.

Definition

Anthrax spores are so small, you may not be able to see, smell, or taste them.

Bioterrorism

A bioterrorism attack is a deliberate release of viruses, bacteria, or other germs (agents) used to cause sickness or death in people, animals, or plants. Anthrax can be released quietly and without anyone knowing. Bioterrorists may send packages or envelopes that contain harmful germs, like in 2001, when anthrax was added to a powder and deliberately spread through the mail.

Anthrax is one of the most likely agents to be used in a biological attack. It only takes a small amount of anthrax to infect a large number of people.

Clue 4

Blood samples tested positive for Bacillus anthracis.

After intense questioning, testing at government buildings, and lab tests, authorities find no evidence of anthrax. The bioterror threat was a hoax.

Meanwhile, the results of the blood tests you sent to the public health labs indicate a need for further testing, so you send them away to special labs at the Centers for Disease Control and Prevention (CDC). The results from CDC labs show Bacillus anthracis, the bacteria that causes anthrax!

Based on this finding and the patients' symptoms, the doctors diagnose each patient with inhalation anthrax. You tell all the patients to begin treatment immediately. But if it's anthrax after all, does that mean the police missed something?

Cases

Zeke learned how to make djembes in Mali.

Since you've ruled out the government building as the place where all of the sick people came in contact with anthrax, you review the attack rates and interviews again. You find that everyone who's tested positive for anthrax also attended a music event at the same Chicago concert hall where Zeke held his music workshop.

Health Tips

Anthrax can be treated with antibiotics.

Treatment of anthrax
Someone with symptoms of anthrax should get medical treatment as quickly as possible to have the best chances for a full recovery. Doctors will use several antibiotics that work best for treating anthrax. They will also consider which antibiotics are best for a patient based on his or her medical history.

Prevention of anthrax
Antibiotics can also be used to prevent anthrax from developing in people who have been exposed but have not yet developed symptoms. Anthrax spores in a person's body typically take 1 to 6 days to be "activated" - to start releasing their toxins - but some spores can take more than a month before they do so. That's why people who have been exposed to anthrax must take antibiotics for 60 days - to ensure anthrax is no longer in their bodies.

Definition

A person can get inhalation anthrax by breathing in anthrax spores.

Inhalation anthrax
If a person breathes in anthrax, they can get inhalation anthrax. When anthrax germs are inside your body, they start to grow and multiply. This could happen quickly or it could take a long time. After the anthrax starts to grow, it releases toxins - or poisons - that will attack your body and make you sicker and sicker.

Early symptoms of inhalation anthrax are much like symptoms of the flu - fever/chills, cough, nausea or vomiting. Other symptoms may include:

• Passing out
• Confusion
• Dizziness
• Trouble breathing
• Chest pain
• Headache
• Sweats (often drenching)
• Extreme tiredness
• Fatigue
• Body aches

Clue 5

All of those with anthrax were in Zeke's music workshop.

All of the people who became sick in this outbreak were together on the day of the workshop. You're now convinced that the workshop is where anthrax was released, though you still aren't sure how.

While you try to figure that out, there's something else you need to do. The 35 workshop participants who are healthy must be given antibiotics to prevent them from becoming sick (this is called post-exposure prophylaxis), since they may have been exposed to anthrax.

You're one step away from finding out what caused the outbreak!

Cases

Zeke used goat skin he brought from Africa to make a drum during his workshop in Chicago.

You talk to Zeke again. He remembers the drum maker in Mali was coughing and having trouble taking deep breaths, similar to the symptoms of all the sick people from the music workshop. You investigate further, contacting health authorities in Mali. They tell you that the drum maker passed away shortly after Zeke returned to Chicago.

Zeke also tells you that during the workshop in Chicago, he demonstrated how to make a drum, using goat skins he brought back from Africa.

You decide to go back to the other participants at the workshop to ask about it. Interestingly, most of the sick people report that while Zeke was showing them how to make the drum, they noticed a large amount of dust and particles floating in the air.

Tip

Anthrax can infect livestock like cattle and goats.

People can get anthrax through contact with infected animals or their products, such as hides or hair. In fact, anthrax used to be called "wool sorters' disease" and was considered a common risk for workers in wool mills, slaughterhouses, and factories that processed animal hides, hair, and bone.

Anthrax is rare in the United States, but outbreaks do occur in wild and domestic animals. Yearly vaccination of animals is recommended in areas that have had anthrax in the past. The disease is most common in parts of Central and South America, sub-Saharan Africa, central and southwestern Asia, southern and Eastern Europe, and the Caribbean.

Clue 1

The villages of Zamfara Province are in a remote northwestern section of Nigeria, far from any city or paved roads.

Doctors Without Borders has been doing some routine health work in northwestern Nigeria. This is a remote area, with dusty and mountainous terrain. People here are very poor. Most are farmers or miners who dig for precious minerals like gold.

The doctors discovered that 3 villages are in the midst of a horrible outbreak: 118 children (many of them younger than 5) are dead. Many more are sick, with symptoms including vomiting, abdominal pain, headache, and convulsions (sudden, violent, uncontrollable shaking).

Clue 2

The Zamfara Province of Nigeria is a very poor, isolated area.

It's a major undertaking, but you and your team make it to the villages. There you find a terrible scene. Outside the villages is a graveyard with more than 100 newly dug, small graves.

Parents of children who died tell you that their kids had seizures, and you see that many of the sick kids are still having seizures. Others are listless, and some have gone blind.

Most of the sick are children. There are some sick adults, too, but they aren't as bad off, and no adults have died.

Notes

After days of traveling through rough terrain, you finally reach the villages.

Just reaching the villages was a huge challenge: after a long flight, you then had to drive for 2 days across hundreds of miles of dirt roads, over mountains, while hauling a huge amount of gear. You had medical equipment, environmental testing equipment, computers, large batteries for power, and more.

GPS doesn't work out here, so simply finding the villages was an adventure. Sometimes you had to follow puzzling directions that people offered, like "turn left at the river."

You also need a team of security guards, and you work closely with the local emir (religious leader) so that people know you're here to help.

Cases

Village children fill water containers at the common village well.

There are 3 villages in this area. Each village consists of open-air dwellings with dirt floors, separated by low walls. People from extended families live in compounds (a number of dwellings close together, enclosed by a common wall).

Some of the compounds have their own well for drinking water, but people in other compounds use a common village well.

A few of the villagers begin to wonder if the drinking water is contaminated.

Clue 3

A medical treatment and supply tent.

Now that you have the village elders' permission, you take blood tests of all the sick people in the village, including children under 5.

While doing your research in the villages, you notice that in many cases entire families are involved in mining. Many children work in the mines and even very young children help their mothers break down rocks or dry the ore in their own family compound.

The blood tests show that the sick children have extremely high levels of lead in their blood, which means they have lead poisoning, a serious and often fatal condition. The sick children need immediate treatment, but you only have a limited amount of medicine.

Cases

The villages involved in mining have far more sick kids.

As part of the investigation, you discover that 1 of the 3 villages is not involved in gold mining and has a much lower rate of sickness than the other 2 villages. This leads you to suspect that the mining is to blame for the lead poisoning, since it releases so much toxic lead dust into the air.

The people who mine gold don't have sophisticated machinery or protective equipment. They collect large rocks and then crush them (with simple tools or their hands) without wearing facemasks, goggles, or gloves. And they don't do this work solely in a mine, either. Much of the work is done in the village, and some is even done in family compounds, by mothers and children.

You try to talk to the head of each household to find out whether the family members have been mining.

Definition

Children under the age of 5 are especially vulnerable to lead poisoning.

What is lead poisoning?
Lead poisoning is a serious condition that occurs when lead builds up in the body. Even small amounts of lead can cause severe health problems. At very high levels, lead poisoning can be fatal.

Children under the age of 5 are especially vulnerable to lead poisoning because it can severely affect mental and physical development. Young children are also more likely to get lead poisoning because they're often on the ground and exposed to lead-contaminated soil and dust. They tend to put their hands in their mouth and nose, increasing their chances of infection.

Lead-based paint and lead-contaminated dust in older buildings are the most common sources of lead poisoning in children in the United States. Other sources include contaminated air, water, and soil.

Clue 4

A mine near a contaminated village.

You start treating the sickest kids with chelation therapy to help them recover.

You've learned that two-thirds of the families in the 2 sicker villages are mining gold. The mining could be responsible for the deaths, but because the villagers are so poor and this is the only way they can make money, they don't want to stop mining.

You need to determine what parts of mining put the villagers at highest risk. When interviewing the families, you ask about the types of mining activities they do. You need to figure out which of these activities are most dangerous.

Definition

Children treated with chelation therapy receive it over the course of many weeks.

What is chelation therapy?
Chelation therapy is a treatment used to address lead poisoning. In Nigeria, doctors used an oral medicine (Succimer), a chemical that binds, or attaches, to heavy metals such as iron, lead, mercury, cadmium, and zinc. The body then removes the chemicals through urination.

Children treated with chelation therapy receive it over the course of many weeks. Children often need more than one dose of chelation especially if their blood lead levels are very high.

Chelation therapy saves lives. The deaths from lead poisoning stop almost immediately as soon as the medicine becomes available. However, it doesn't reverse any damage that has already been done to the child's brain. Some children are blind, have paralysis or major seizure disorders that could be permanent.

Data

Tip: To identify the likely source of the outbreak, look for a high attack rate among those who performed a specific activity and a low attack rate among those who did not.

There are several steps to mining the gold. Some people break the rocks into smaller gravel, some grind the rocks into a fine powder, some wash and dry the ore powder to separate the gold out, and some use heat to vaporize the mercury out.

To figure out which steps are most dangerous, you have a talk with mothers who have healthy children as well as mothers who have sick children. In all, you gather data about 52 healthy kids and 50 sick kids. Then, you ask the parents about each mining activity they do so you can calculate the "attack rate" for each activity.

Clue 5

A sample of the potentially deadly lead-filled ore.

Four weeks after arriving in the villages, you've given chelation therapy to the sickest kids younger than 5. Most of them have improved, though many may still have permanent disabilities. Teams of Nigerian workers and environmental specialists thought it was best to remove the top layer of contaminated earth from the villages to reduce the number of people who get sick, so it was removed and buried far outside the village. They had to hurry, because the rainy season is coming, and such work will be impossible then.

You've been working hard to educate the miners about the risks of this kind of mining. You tell them not to mine from inside their own compounds. They should always keep their living areas free of mining activities.

Still, they don't have good protective equipment. And even when they follow your advice, most of the miners come home covered in dust, tracking the dust when they walk to and from the village.

Data

You've kept careful track of how many people got sick.

You've kept careful track of the number of cases since the epidemic started by using an epi curve. An epi curve shows how an outbreak changes over time. It includes:

• Date when a person became sick.
• Number of people who became sick on each day.

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

Learn how to read an epi curve.

Health Tips

People removing old, lead-based paint must take care not to release lead dust into the air.

In this outbreak, lead dust from the mines was to blame. However, in the US, when children have high blood lead levels, it's usually because of lead-based paint (which was banned from use in housing in 1978) and lead-contaminated dust. To avoid lead poisoning in the US, follow these tips:

• Make sure children do not have access to peeling paint or chewable surfaces painted with lead-based paint.
• Regularly wash children's hands and toys. Hands and toys can become contaminated from household dust or exterior soil. Both are known lead sources.
• Create barriers between living/play areas and lead sources.
• Prevent children from playing in bare soil; if possible, provide them with sandboxes.
• Pregnant women and children should not be present in housing built before 1978 that is undergoing renovation. They should not participate in activities that disturb old paint or in cleaning up paint debris after work is completed.
• Household dust is a major source of lead, so parents should wet-mop floors and wet-wipe horizontal surfaces every 2-3 weeks.

Clue 1

Doctors aren't sure what's causing this serious illness.

It's late August, and New York City is baking in a heat wave. Fred is a retired US veteran in his 70s and quite active for his age. He's an avid gardener and likes going for long walks every day.

Fred started feeling sick 5 days ago, and now he's in the hospital with a high fever, bad headache, and extreme muscle weakness. He's having so much trouble breathing that he's been put on a ventilator.

His doctor conducts tests that suggest Fred has a virus, although it's not yet clear what kind of virus. The next day, 2 people in their 60s with similar symptoms are admitted to the hospital.

Cases

The sick people all live in the Queens borough of New York City.

New York City's Department of Health has reached out to all local hospitals to see if anyone else has been admitted with high fevers and headaches. As it turns out, a total of 11 people are hospitalized with similar symptoms, and they all live in northern Queens. Of the 11 cases, 9 live in the same general neighborhood, and the other 2 live only a short distance away.

Overall, 8 of the 11 are 55 years or older. Most of them had been relatively healthy until getting this sickness, although 2 had recently returned from hospital stays (one after having hip replacement surgery and the other after having a skin lesion removed).

Clue 2

The outbreak is spreading; 17 people are now sick, 3 are in critical condition, and 1 has died.

Sadly, Fred dies in the hospital, as does another sick person. Three others are in critical condition, with very high fever, headache, disorientation (confusion), muscle weakness, and convulsions (sudden, violent, uncontrollable shaking).

The outbreak is getting worse. There are now 17 sick people, all of whom live in northern Queens.

You talk to the sick people and their relatives to find out what they had been doing in the days before they got sick. You visit their homes and investigate their environments, searching for clues.

Blood samples from the patients are sent to the New York State Health Department laboratory where they will run tests to see if they can identify what may be making these people sick.

Data

What do most of the sick people have in common?

You visit with the sick people and their families, asking questions like:

• When did you first get sick?
• Have you traveled much recently?
• What have you had to eat in the last 5 days?
• Have you taken any drugs in the last 5 days? If so, what?
• What kinds of animals have you been around lately?
• Do you spend a lot of time outside? How about in the evening?
• Are any of your friends or relatives sick, too?

Notes

Lots of dead crows are showing up on city sidewalks.

You've been hearing reports that an unusual number of dead crows are being found in the city. You don't have any reason to believe that this is connected to your investigation, because none of the sick people mention having been near birds lately.

Still, you make a point of staying in touch with local veterinarians who are trying to find out why the birds died.

Clue 3

These tiny creatures are causing big problems.

Many of the sick people said they'd recently spent time outdoors in the evening (walking or gardening). In talking with the sick people, many confirm that they were bitten by a mosquito in the last week, although others can't quite remember.

This evidence, along with test results from the laboratory that suggest infection with a mosquito-transmitted virus, leads you to believe that the sick people have St. Louis encephalitis, a rare disease that caused another outbreak in New York back in the 1950s.

Bad news: the outbreak is spreading to other areas! You learn that 2 people in the Bronx have what appears to be the same illness, as does someone in Manhattan and someone in Westchester County, north of the Bronx. Two of these people say they've been to Queens recently. And you also get an update about all those dead birds.

Definition

Electron micrograph of the St. Louis encephalitis virus, as seen in a mosquito salivary gland.

What is St. Louis encephalitis virus?
St. Louis encephalitis virus is transmitted to people by the bite of an infected mosquito. Most people infected with St. Louis encephalitis virus have no apparent illness, but some people do get quite sick. Initial symptoms include:

• Fever
• Headache
• Nausea
• Vomiting
• Tiredness

In rare cases, St. Louis encephalitis virus can kill or cause long-term disability. Severe illness occurs more commonly in older adults.

There is no specific treatment for St. Louis encephalitis virus infection. You can reduce your risk by using insect repellent, wearing protective clothing, and staying indoors in the evening when mosquitoes are most active.

Notes

Several exotic birds, including flamingos, have died at the Bronx Zoo.

The reports about dead crows keep coming. The Bronx Zoo calls to say that several of their birds have also died in the last 3 days, including exotic species like Chilean flamingos. But St. Louis encephalitis virus doesn't kill birds, so you assume that this is an unrelated disease.

To be safe, you talk to the team of veterinarians who took lab samples from the dead birds. The cause of death still hasn't been determined, so they're still investigating and will update you with any news.

Health Tips

Your home has several places where mosquitoes might try to lay eggs.

You can help reduce the number of mosquitoes in outdoor areas where you work and play by draining sources of standing water. These are places where mosquitoes lay their eggs and breed.

• At least once or twice a week, empty water from flower pots, pet food and water dishes, birdbaths, swimming pool covers, kiddie pools, buckets, barrels, and cans.
• Check for clogged rain gutters and clean them out.
• Remove discarded tires and other items that could collect water.

Local mosquito control organizations may also spray insecticides to help further reduce the number of mosquitoes in your neighborhood.

• Support your local community mosquito control programs.
• Use mosquito repellents when you go outdoors.

Note: Vitamin B and "ultrasonic" devices are not effective in preventing mosquito bites.

Clue 4

The virus has spread across the entire city.

Lab tests on the dead crows show that they have West Nile virus, which has never been found in the Western Hemisphere before!

Knowing this information, you decide to run a different test on the sick people. You learn they don't have St. Louis encephalitis virus after all; they have West Nile virus. West Nile virus is closely related to St. Louis encephalitis virus and causes a similar illness. Since West Nile virus has never been seen in the United States before, the clinical findings and lab tests could be confusing.

Mosquitoes spread West Nile virus to people, but mosquitoes can also spread it to birds. This is why the birds started dying at about the same time that so many people got sick.

Now that you know West Nile virus has come to the United States, you need to take some steps to prevent it from spreading even more!

Definition

Photomicrograph of brain tissue from a West Nile virus encephalitis patient.

What is West Nile virus?
West Nile virus disease is a potentially serious illness spread by mosquitoes. Before 1999, West Nile virus had never been found in the Western Hemisphere. Although it's not clear how the virus came to our area, experts believe West Nile virus disease is now a seasonal epidemic in North America that flares up in the summer and continues into the fall.

People typically get symptoms 4 to 10 days after they are bitten by an infected mosquito. West Nile virus affects everyone differently:

• About 4 in 5 people who are infected will not show any symptoms at all.
• Up to 1 in 5 people who become infected will have symptoms such as fever, headache, body aches, nausea, vomiting, or a rash. Most of the symptoms last for a few days. In some people, fatigue may linger for several weeks.
• A small number of people (about 1 in 150) will develop severe illness. These severe symptoms can include disorientation, coma, convulsions, tremors, and paralysis. These symptoms can last several weeks, and some damage to the brain and nerves may be permanent.

Cases

Mosquitoes can carry many different diseases, including West Nile virus. Are the insecticides working?

You work with city, county, and state authorities to set traps that will collect mosquitoes from across the area.

You test the mosquitoes for various viruses, including West Nile virus. You have already begun a carefully targeted program of spraying insecticides in northern Queens and the neighboring south Bronx to cut down on the mosquito population, decreasing the possibility that West Nile virus will spread.

The city sprays insecticides on September 10 (about 3 weeks after you were first called in). The surrounding areas are sprayed on September 14. During the next few days, a few more people get sick. You need to figure out if the insecticides are working or if the illness is still spreading. If it is, you'll need to try something else to stop the spread.

Data

You need to figure out if the insecticides have helped contain the outbreak.

To keep track of the outbreak, you've created an epidemiologic (epi) curve. This shows Disease Detectives how an outbreak changes over time. It includes:

• Date when a person became sick.
• Number of people who became sick on each day.

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

Learn how to read an epi curve.

Clue 5

Most people are infected with West Nile virus from June through September.

As October begins, a total of 62 people have gotten sick, and 7 have died. All of the people who died were in their 60s or older. Blood tests you've taken of other New Yorkers show that many other people have been infected with the virus, too, but they never showed any symptoms. As has been the case in other countries, only a small percentage of the people infected with West Nile virus actually became sick.

Now that the weather has gotten cooler, mosquitoes have stopped biting people in New York and other northeastern states. We may never know how West Nile virus first came to the United States, but odds are good that it will reappear next spring when mosquitoes return.

Notes

Infected migrating birds may have first brought West Nile virus to the United States.

There are a few theories to explain how West Nile virus came to the United States:

• Infected migrating birds brought the virus to New York City.
• Infected birds may have flown to or been transported to the United States.
• Virus-infected mosquitoes may have been brought accidentally to the United States on boats or planes from other countries.

Health Tips

Be sure to apply insect repellent to exposed skin.

Mosquito bites are more than an itchy pain. They can also spread serious illnesses. Follow these steps to avoid bites:

• Apply insect repellent to exposed skin.
• When weather permits, wear long-sleeved shirts and long pants when outdoors.
• Place mosquito netting over infant carriers when you are outdoors with infants.
• Consider staying indoors at dawn, dusk, and in the early evening, which are peak mosquito-biting times.
• Install or repair window and door screens so that mosquitoes cannot get indoors.
• Spray clothing with repellents containing permethrin, since mosquitoes can bite through thin clothing. Do not apply repellents containing permethrin directly to your skin.

Clue 1

Conference attendees sitting in sessions.

You are on a mission to stop this outbreak! First, you call the event coordinator and ask for a schedule of events and a list of the conference attendees. The coordinator also gives you contact information for the 15 people she knows who are sick so far.

You begin by attempting to call each sick person to interview them and ask about their symptoms, when they first became sick, which events they attended at the conference, what they ate and drank while at the conference, and if they know of others who are sick. Since you don't have any lab results yet, you need other information to come up with a hypothesis (an idea or theory) about what is making people sick and what these people have in common.

Later, you'll need to find out:

• How many people are sick?
• What are the signs and symptoms of those who are sick?
• When did the illness begin?
• What do the individuals have in common?
• Which events did each of the sick people attend?

Data

List of activities in which the 10 sick people participated.

You succeed in reaching 10 of the 15 sick people. To better understand how the attendees got sick, you ask about the activities in which they participated since arriving at the conference.

You also ask about the foods they ate, drinks consumed, as well as other activities that might have put them at risk.

You then study the data to see what the sick people have in common.

Clue 2

The good news is most of the people who are sick are starting to get better. In talking with a few of the attendees, you learn that most of them met a lot of new people at the Welcome Party, shook hands, and ate some food.

Based on what they've told you about the party, you suspect something the participants ate at the Welcome Party is causing everyone to be sick. However, in order to be certain you'll need to interview as many of the conference attendees as possible.

The conference organizer tells you the food at the Welcome Party was prepared by a local caterer. You request a copy of the menu served at the Welcome Party in order to develop a list of items to which participants might have been exposed.

Data

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

During your initial 10 interviews you asked about attendee participation in various conference events, as well as the food items they ate during conference events.

Using the information gathered from the interviews, along with the Welcome Party menu, you create a standard questionnaire that you use to interview as many of the 75 conference attendees as possible. You make sure to ask clear, detailed questions about any items you suspect.

By interviewing most of the 75 conference attendees, you learn that at least 25 people are sick, including your 10 initial interviewees. A few individuals began feeling ill on Monday, with many more reporting symptoms on Tuesday and Wednesday.

You don't have laboratory test results yet, so you define a sick person as someone who attended the conference and began having diarrhea anytime between Jan. 29 through Feb. 5.

To analyze the data, you create an epidemic curve or "epi curve" which shows how an outbreak changes over time. It includes:

• Date when each person became sick.
• Number of people who became sick on each day.

Learn more about an epi curve.

Cases

Attack rates based on the interviews with the conference attendees.

After conducting these additional interviews, you calculate the attack rate and relative risk of each conference event and each menu item from the Welcome Party.

Based on the interviews, you confirm your initial hypothesis that the illness was associated with the Welcome Party and not any of the other conference events. You therefore focus on determining the attack rates of the food items at the party.

Notes

Hint: A relative risk greater than 1 indicates that people exposed had a greater chance of getter sick than those not exposed.

Relative risk is a measure of association that helps you to determine which items are most likely responsible for an outbreak. It allows investigators to compare risk factors or exposures among those who are sick, compared with those who are not.

Since you have identified the Welcome Party as the source of illness, you now focus on the relative risk of the food items served at the party.

Clue 3

Leftover spinach from the hotel kitchen. FDA is the federal agency responsible for regulatory oversight related to spinach.

Initial laboratory results are back and show that the outbreak is likely due to E. coli O157. The state health department has to confirm the results in their lab, but that could take several days.

In the meantime, you ask the caterer for a list of the recipes from the Welcome Party and review the ingredients. You notice that the 2 dishes with the highest relative risks (the spinach dip and veggie lasagna) both had raw spinach leaves added as a garnish after the dishes were cooked; no other dishes used raw spinach and there were no other common ingredients between these 2 dishes. You immediately contact the Food and Drug Administration (FDA) and tell them about your suspicions that raw spinach could be the source of this outbreak.

You don't have any time to waste, so you go visit the caterer. Luckily, you find some unopened bags of fresh spinach that were purchased at the same time as those used to prepare the food for the Welcome Party. Since the spinach is still in the bag, FDA is able to trace the lot numbers for this product to find out where it was grown and bagged.

Definition

E. coli O157:H7 from an electron micrograph under high magnification.

What is E. coli?

Escherichia coli (abbreviated as E. coli) are bacteria found in the environment, foods, and intestines of people and animals.

Most E. coli are harmless and actually are an important part of a healthy human intestinal tract. However, some are pathogenic, meaning they can cause illness, either diarrhea or illness outside of the intestinal tract. The types of E. coli that can cause diarrhea can be transmitted through contaminated water or food, through contact with animals or their environments, or when infected people do not wash hands well after going to the bathroom, and the bacteria get from their hands into someone else's mouth.

Some kinds of E. coli cause disease by making a toxin called Shiga toxin. The bacteria that make these toxins are called "Shiga toxin-producing" E. coli, or STEC. The most commonly identified STEC in North America is E. coli O157:H7.

• People infected with E. coli O157:H7 usually get sick within 2 to 8 days (average of 3 to 4 days) after swallowing the organism. Most people develop diarrhea (usually watery and often bloody) and stomach cramps. Most illnesses resolve on their own within 7 days. Some illnesses last longer and can be more severe.
• Hemolytic uremic syndrome (HUS), a type of kidney failure, can begin as the diarrhea is improving. HUS can occur in people of any age but is most common in children under 5 years old and the elderly.

Get tips on how to stay safe.

Health Tips

When washing hands, wet hands, use soap, rub hands together for at least 20 seconds to lather, and then rinse under running water. Dry with a clean towel or air dry.

The best way to protect yourself from an E. coli infection is to:

• Wash your hands thoroughly after using the bathroom or changing diapers and before preparing or eating food. You should also wash your hands after contact with animals or their environments (at farms, petting zoos, fairs, even your own backyard). This is important even if the animals appear healthy because they can still be shedding germs that can make you sick.
• Cook meats thoroughly. Ground beef and meat that has been needle-tenderized should be cooked to a temperature of at least 160°F (70°C). It's best to use a thermometer, as color is not a very reliable indicator of "doneness."
• Avoid raw milk, unpasteurized dairy products (like raw milk soft cheeses), and unpasteurized juices (like fresh apple cider).
• Avoid swallowing water when swimming or playing in lakes, ponds, streams, swimming pools, and backyard "kiddie" pools.
• Prevent cross-contamination in food preparation areas by thoroughly washing hands, counters, cutting boards, and utensils after you touch raw meat.

Notes

Lot numbers are usually found stamped on the outside packaging (not as part of the label) since lot numbers change with each batch.

What is a Lot Number?

A lot number is an identification (ID) number given to each batch of a product (or subset of a batch). When manufacturers produce a product, they give each batch a unique lot number so that it is possible to track the product, including the ingredients used, the manufacturing plant, and the equipment used to process an item.

Lot numbers help with tracing and may even help you find the specific farm or field where the produce was grown and processed.

Clue 4

Digitally colorized image of E. coli O157:H7 under the high magnification of a scanning electron micrograph.

The results from the state health department are in! The bacterial testing shows the sick people are, in fact, infected with E. coli O157:H7.

The State Public Health Laboratory sends the DNA "fingerprints" to PulseNet (a national network of state and local public health laboratories and federal food regulatory laboratories).

PulseNet scientists at CDC headquarters in Atlanta compare "fingerprints" of this strain of E. coli O157 with the DNA "fingerprints" in the database and find that this particular strain is indistinguishable from that of 12 other cases that have been reported across the country in the last few weeks. You also discover that this strain has never been reported to PulseNet before now.

Cases

This map shows the number of persons infected with the outbreak strain of E. coli 0157:H7 across the US. The states that are darker have a larger number of people sick.

In fact, there is already another ongoing investigation of these 12 sick people. You learn from the EIS officer at CDC headquarters that they are already investigating this outbreak. They also tell you that 3 additional people have been hospitalized and 1 person has died.

In total, 37 people are infected with the outbreak strain from 5 different states. Twenty-five people were infected during the conference in Georgia, and another 12 people are spread across the country:

• California: 2
• Georgia: 25
• MIssouri: 2
• Tennessee: 5
• Utah: 3

Clue 5

FDA is investigating all possible points of contamination.

Your hunch is right! The initial interviews from the state and local investigators reveal 11 of the 12 other sick people ate spinach, too. To find out if these people ate the same brand of spinach as those at the conference, you need to review the data collected during all of the interviews.

In the meantime, FDA visits the production facility where the spinach used at the conference event is cleaned and bagged. During their visit, FDA officials look at the possible points of contamination (such as dirty wash water, sick employees handling the spinach, or other problems). However, no likely points of contamination are found.

FDA decides to visit the spinach farm. Now this is a "field" investigation!

Data

Fresh, uncooked spinach.

You review data collected from interviews with each of the 11 additional sick people to find out if they ate the same brand of spinach that made conference attendees sick. You want to learn more about when and where they might have eaten it, including if they ate the spinach at home or in a restaurant. If the spinach was eaten at home, you'll also want to know what brand it was and from where it was purchased.

Based on your data review, you discover all of the people who are sick ate the same brand of spinach as the attendees from the conference. Fortunately, 2 of the individuals still have some of the spinach, so you collect the spinach to check the lot number and test it for E. coli O157:H7.

Not only do the lot numbers match the bags of spinach from the conference caterer, but lab testing of these new bags of spinach finds they were also contaminated with E. coli O157:H7.

Notes

Cattle from the nearby farm.

During the visit to the spinach farm, the farm manager is interviewed so data can be collected about the farm and its operations.

The spinach farm is next to a creek. Across the creek, about a quarter a mile away, there is a farm with 300 cows The pastures the cows graze in is a very hilly area that is on higher ground.

There is a well maintained fence to keep the cows out of the fields and away from the creek. The spinach farmer reports that he uses treated well water for his crops, but there has been some flooding in parts of his fields due to recent heavy rains.

Tip

Cattle from the nearby farm.

Did you know that cattle are natural carriers of E. coli O157:H7?

Cows do not always carry E. coli O157, but sometimes they do.

Although cows are usually not affected by the bacteria, they can carry it and shed it in their waste, even while appearing healthy. If the bacteria got into the spinach fields, it could contaminate the spinach.

Clue 1

It's a hot summer in southern Louisiana.

The workers reported to the sugar plantation for their first day on July 9. After 2 days on the job, 7 workers went to the doctor complaining of headache, fatigue, and muscle aches. Six of them have fevers. The doctor told them to take some painkillers and get some rest.

A couple of days later, one of those sick workers, a 20-year-old named Jorge, had to be taken to the nearest hospital. His left shoulder and arm were in a lot of pain, and his hand was numb. The manager just thinks his new workers are faking to get out of work, but one doctor thinks it could be a meningitis outbreak.

Notes

Tractor pulling sugarcane.

The temperature has been over 100 degrees since the beginning of July, and the humidity makes it even worse. Mosquitoes are thick in the air, and venomous snakes slither in the grass. Some of the workers have had to watch out for stray dogs that wander onto the plantation.

The workers share water bottles in the field, and many of them take dips in a nearby lake to cool off after work.

Definition

Meningitis can sometimes be caused by a fungus, as was the case in a 2012 outbreak.

What is Meningitis?

Meningitis is a disease caused by swelling of the meninges, which are membranes that cover the brain and spinal cord. The swelling is usually a result of an infection of the fluid around the brain and spinal cord.

Meningitis is most often caused by bacteria or viruses. Meningitis also can be caused by physical injury, cancer, certain drugs, or even parasites.

Health Tips

Swimming in warm bodies of water can sometimes cause disease.

Swimming in warm water (lakes, ponds, and pools) can put you at risk of recreational water illnesses (RWIs). These are caused by germs spread when people swallow or come into contact with contaminated (dirty) water.

RWIs include many different kinds of infections, affecting skin, ears, eyes, digestive systems, and the brain. Diarrhea is the most common symptom of RWIs.

Clue 2

Many of the workers live in cramped apartments or on the plantation.

Four more workers are sick on July 13, bringing the total to 11. You interview the sick workers and their manager to get more information.

The workers were split into 3 groups on 3 different fields. Some shared water bottles while they worked, and some swam in the lake afterwards. Some of the workers live in the town year-round, but many came from other parts of the state and even other countries.

Most live in cramped apartments, sharing bedrooms. A few sleep in small trailers on the plantation property.

Data

You gather more information about what the sick people had been doing.

Of the 11 who are sick, 6 recently traveled from another country (4 are from Mexico and 2 are from Guatemala). Jorge, who's from Guatemala, is the only one in the hospital.

Eight of the sick workers have worked on this plantation in past summers, and they don't think the hard work or the heat has anything to do with why they've gotten sick.

Clue 3

Jorge has been transferred to the intensive care unit.

Doctors confirm that the other workers just had a bad virus, but Jorge seems to have something worse. Ten of the workers are feeling better on July 20, and have returned to work.

Jorge, however, has gotten worse: one of his eyelids is drooping, he hasn't been able to move his right arm for days, and he's had so much trouble breathing that he's been put on a breathing tube. On July 21, which is 10 days after he first felt sick, he slips into a coma. His symptoms suggest it's something affecting his nerves and brain.

Cases

You trace Jorge's steps from Guatemala to Louisiana

Based on his symptoms, Jorge's doctors now think that he could have rabies, which is almost always caused by the bite of a rabid animal. There's a small scar on one of his shoulders that could be a bite mark. The doctors run some tests to confirm their suspicion, and you send the lab work to the Centers for Disease Control and Prevention (CDC) headquarters in Atlanta to analyze.

You also talk to a worker named Eduardo, who is from the same town in Guatemala as Jorge. He tells you that they left their town together on July 2, riding buses and trains through Guatemala and Mexico for 4 days. They spent the night in a small town in Texas and made it to the plantation on July 8.

He doesn't remember Jorge saying he'd been bitten by any animals, but he does tell you that there were a lot of stray dogs near the field where they were working.

Definition

A photomicrograph of the rabies virus.

What is Rabies?

Rabies is a virus most often spread by the bite of a rabid animal. The vast majority of rabies cases in the US happen in wild animals like raccoons, skunks, bats, and foxes.

The rabies virus infects the brain and nerves. People who get rabies usually have the virus in their bodies for many weeks before they show any symptoms. The early symptoms are like those of many other illnesses: fever, headache, and weakness or discomfort.

Over time, more symptoms show up: confusion, hyperactivity, trouble sleeping, slight or partial paralysis, hallucinations, hypersalivation (increase in saliva), difficulty swallowing, and fear of water. Within days of these symptoms, the person dies. Because there's no cure for rabies, people who have been bitten by a potentially rabid animal, need to seek medical care immediately, before the virus can travel to their brain.

Clue 4

Bats are a common carrier of rabies.

The test results confirm that Jorge has rabies. When you call Jorge's mother in Guatemala, she tells you that he had been bitten by a vampire bat in May. A growing number of people in her town have been getting rabies, she says. Because Jorge's symptoms are so far along, unfortunately, there's little doctors can do to save him. On July 26, he dies in the hospital.

The key to preventing rabies after someone has been bitten is to give a series of shots called post-exposure prophylaxis (PEP) before the person has any symptoms. That means you have another big decision to make.

Cases

In the US, most people who get rabies catch it after being bitten by a rabid animal. Scientists have proven that it is possible to catch rabies through the saliva of an infected person.

There could be more infected people who aren't showing any symptoms yet. Because rabies is a fatal illness, anyone who might be at risk should get the PEP shots as soon as possible.

You know that Jorge traveled for days with Eduardo, lived in an apartment with 3 other people, and worked in the fields with other workers. He even shared his water bottle with some of them. You need to make sure none of these people get sick.

Health Tips

Make sure your dogs and cats are vaccinated for rabies.

How to prevent rabies:

• Take your pet dogs and cats to the veterinarian regularly and keep them up-to-date on rabies vaccinations.
• Maintain control of your pets: keep cats indoors, and keep your eye on dogs.
• Spay or neuter your pets to help reduce the number of stray, unvaccinated animals.
• Call animal control to remove all stray animals from your neighborhood, since they may be unvaccinated or ill.
• Children are often at greatest risk from rabies, since they're more likely to be bitten by dogs. Keep them away from wild or unfamiliar animals.
• Be especially careful around animals when traveling to other countries, as they don't always have access to PEP.

Clue 5

Many people in the village have gotten rabies in the last 2 years.

As you work with health authorities in Guatemala, you learn that Jorge's mother was right: 11 people in his town have come down with rabies in the last 2 years. That's odd, because there had never been any cases in this town before.

The Guatemalan health department invites you to come down and investigate. This is a small village in the mountains, and it's only had electricity for about 2 years. Many of the cows and donkeys on local farms have bat bites, and so do some dogs.

Notes

Why have bats started biting people in the village?

You study where the vampire bats live and which farm animals have been bitten. You also notice that though the village recently added electric lights down its small roads, people still don't have electricity in their homes. Vampire bats prefer to feed in darkness.

It's possible that the new lights have disturbed the bats' usual patterns, which is why they've started coming to this town. Since the houses are still dark, the bats are flying in and biting people while they sleep.

Clue 1

Eye doctors suspect an increase in a rare infection.

Dr. Lee is an ophthalmologist (eye doctor) in Athens, Georgia. He recently noticed that more of his patients were getting a rare disease called Acanthamoeba keratitis (known as "AK"). There wasn't a sudden rise in the number of cases; in fact, the increase was so gradual that he only realized it after several years.

He calls the Georgia Department of Public Health, and it turns out he isn't the only doctor suspecting an increase. Three other doctors have recently called about the same thing. The Department then calls the Centers for Disease Control and Prevention (CDC) and asks you to figure out what's going on, and fast!

Data

You plot data from 5 states to see if AK is increasing across the country.

Soon after the call from Georgia, New York's Department of Public Health calls you about the same thing. It's strange that two states nearly 1,000 miles from each other could have the same problem. You wonder if AK is increasing around the country, or if this is a false alarm. It's possible that a few doctors just happen to have sicker patients than other doctors.

You decide to gather 6 years of medical records from a sample of eye doctors in Georgia, New York, and 3 other states across the country to see if AK really is becoming more common.

Definition

A photomicrograph of Acanthamoeba.

What is Acanthamoeba keratitis?

Acanthamoeba is a microscopic ameba ("amoeba" is the British spelling) that can cause rare but severe infections of the eye, skin, brain, and spinal cord.

One of the diseases it causes is Acanthamoeba keratitis (AK), an infection of the eye that causes eye pain, redness, sensitivity to light, and the feeling that something is stuck in your eye. AK can permanently damage your vision or cause blindness.

The ameba is found around the world in soil and dust, as well as in water. It lives in the ocean and freshwater lakes and rivers. It can also be found in swimming pools, hot tubs, and drinking water. Most people will be exposed to it during their lifetime, but very few will become sick from it.

Clue 2

Nearly all of the people infected with AK wear contact lenses.

In order to figure out why so many people are getting AK, you need to learn more. You and a team of Epidemic Intelligence Service (EIS) officers take a closer look at the medical records for all the AK case patients, this time expanding to 10 states. This additional work takes some time, but once you've got all the information you have a better sense of what's happening.

It turns out that 97% of the infected people wear contact lenses. For comparison, only 13% of all Americans wear contacts.

Cases

Many of the people with AK are in their teens or 20s.

You take a look at the medical records for all 1,128 people with AK in 10 states. A typical example is Justin, a 19-year-old college student in Syracuse, NY, who has been wearing contacts for 2 years. He stays up late and sometimes falls asleep in his contacts. Four months ago his right eye started to feel sore, and it looked red. He started using rewetting drops, but they didn't help.

So he stopped wearing contacts for a few days. He didn't want to spend money on the doctor and was hoping the problem would just go away. Instead, it got worse: his vision became blurry.

He finally saw his doctor a month after the problem started, and the doctor told Justin he had AK. Unfortunately, the infection had gotten so bad that Justin will never have normal vision again unless he has corneal transplant surgery.

Data

More than half of the people with AK are either younger than 20 or older than 60.

Of the 1,128 people with AK:

• 359 (32%) are younger than 20.
• 107 (9%) are age 20-29.
• 115 (10%) are age 30-39.
• 117 (10%) are age 40-49.
• 175 (16%) are age 50-59.
• 255 (23%) are older than 60.

Clue 3

Microscopic image of an eye infected with AK.

You decide to find out what contact lens products the people infected with AK use. There are different brands of lenses, different types of lenses (like soft lenses or hard lenses, extended wear, and disposable), and different types of solutions (like disinfecting solutions and rewetting drops).

You also ask the infected people how they use their lenses. Do they ever forget to take their contacts out at night? Do they wear them for too long before replacing them? Do they ever use expired solution?

You and your EIS team review the data to see what's causing the outbreak.

Data

Hint: To find a possible source of the outbreak, look for both a high attack rate for those who participated in an activity and a low attack rate among those who did not participate.

Of the 1,128 people with AK infection, you interview a sample of 194 people who wear contacts. You also talk to 410 people who wear contacts but don't have infections. In outbreak investigations, we call this second group the "control group."

Each person was asked what they did in the month before becoming infected. The "attack rate" was calculated for each activity.

Clue 4

Lab work on Solution D doesn't show that the bottles are contaminated.

Hundreds of people around the country are becoming blind because of AK, and most of them will need surgery to be able to see again. Doctors are alarmed and need to know what's going wrong.

The good news is, you finally have a solid lead! Since you know that many of the people with AK used Solution D, you immediately test the solution for Acanthamoeba.

But it's a dead end. Surprisingly, you don't find the ameba in any of the new bottles you test. Maybe the contact solution isn't to blame. Something else must be causing the increase in AK. Keep investigating!

Cases

This pie chart shows you how long the people with AK have been wearing contacts.

When you first looked at the medical records, you noticed that many of the people with AK were either elderly or teenagers, but you weren't sure what that meant.

Then, when talking again to Dr. Lee and some of the other doctors, they mention that Solution D is marketed toward new contact users. In fact, these doctors even give out a free sample of Solution D as part of their "How to Wear and Care For Your Contact Lenses" packets to patients who are first-time contact lens wearers.

You decide to take another look at your data. Interestingly enough, you find that two thirds (66%) of infected people have been wearing contacts for less than 3 years.

Tip

A scanning electron micrograph (SEM) of an Acanthamoeba polyphaga organism.

Acanthamoeba is usually present in the water and soil. There are a number of ways people can be exposed to Acanthamoeba, but it's usually through water. You wonder if Acanthamoeba has become more common in the country's tap water over the years.

While you're interviewing people, you find out that a separate team from the environmental health department has been testing, for years, the tap water in some of the states you're studying. Their lab results show that the tap water in those states doesn't have any more Acanthamoeba now than it had in the past 15 years. So, exposure to tap water alone isn't causing these infections.

Clue 5

People's behavior with their contacts must play a role in the outbreak.

Now it's starting to make sense! You know that 66% of the infected people are new to wearing contact lenses, and sometimes people who are new at something don't quite know how to do it well. Since you also know that Acanthamoeba is usually spread through water, you suspect that perhaps the new contact lens wearers are letting their lenses touch water or aren't taking proper care of them.

You ask the infected people and your control group another series of questions, this time about their daily routine and habits with their contacts.

Data

You ask the infected people about their contact lens habits.

You ask questions about whether people are doing something that might put them at greater risk of infection, such as:

• Not washing their hands properly before handling their contact lenses.
• "Topping off" their cleaning/disinfecting solution (adding fresh solution to used solution in the contact lens case).
• Storing their contact lenses in water instead of solution.
• Letting water touch their contact lenses at the sink.
• Showering, bathing, or swimming while wearing contact lenses.

Health Tips

People need to disinfect and store their contacts with care to avoid infection.

Contact lens users should follow these guidelines to avoid infections:

• Remove contact lenses before any activity involving contact with water, such as showering, swimming, or using a hot tub.
• Before handling contact lenses, wash your hands with soap and water, then dry them completely.
• Clean contact lenses according to instructions from your eye care provider and the manufacturer's guidelines.
• Never reuse or "top off" old disinfection solution, or add new solution to old solution in a contact lens case.
• Never use saline solution or rewetting drops to disinfect lenses. Neither solution is an effective or approved disinfectant.
• Clean, rub, and rinse your lenses each time you take them out to remove harmful microbes and residues.
• Store lenses in their proper contact lens case.
• Rub and rinse contact lens cases with contact lens solution (never use tap water), then empty them and leave them open to dry.
• Replace your contact lens case at least once every three months.
• Visit your eye care provider for regular eye examinations.
• See your eye care provider if you have any eye pain or discomfort. Eye infections can be serious.

Clue 1

Why are so many military veterans dying?

On July 27, a retired Air Force Captain returned home tired and sick after a trip to Philadelphia. Three days later, he was rushed to the hospital with chest pains, fever, and trouble breathing. He soon died.

Within a week, 10 more Pennsylvania veterans have died, and the state Department of Health calls to ask for your help. You and a large team of Epidemic Intelligence Service (EIS) officers race to Philadelphia, where the city is in a panic and all types of theories are being debated. You start gathering data about when people got sick.

Tip

A new kind of flu was discovered at a nearby army base.

Some of your coworkers are worried this is the start of a new flu epidemic! Older people often get pneumonia from a bad flu, and a few months ago a deadly kind of flu was discovered at a military base only 40 miles from Philadelphia.

Another theory is that it's a terrorist attack, since it's mostly military veterans who are sick. Some people think it could be a rare disease spread by city pigeons, others think it's poisoning from nickel.

Reporters are anxious to know what's happening, and they're following your every move. Well, almost: they're so scared about getting sick themselves that they don't follow you into any hospital rooms.

Data

The number of sick people peaked July 25-27.

Currently 151 are sick and 11 have died, though doctors are warning that many others are near death. Many of the sick are older and most are men. Though they live all over Pennsylvania, they were all in Philadelphia during July 21-24. Many of them were at a military veterans' conference.

• Chest pains
• Fever (as high as 107 degrees)
• Cough
• Pneumonia

To keep track of the data, you make an epidemic curve (epi curve).

Definition

Disease Detectives use epi curves to study how many people become sick each day. Epi curves are updated as new data are gathered.

What's an epidemic curve (epi curve)?

An epi curve shows how an outbreak changes over time. It includes:

• Date when each person became sick.
• Number of people who became sick on each day.

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

Learn how to read an epi curve.

Clue 2

Local hospitals are filling up.

The pressure on you is building. There are now 200 sick people (147 of them are in the hospital), and 23 more people have died! To stay on top of things, you ask a team of nurses to check in with every hospital in the state daily. You also set up a hotline for people to call with tips and information.

You and a team of EIS officers spread out across the city, and place calls all over the state, to talk to 200 sick people and their families. You ask about their symptoms to make sure they all have the same illness. You also need to find out what they did while in Philadelphia in order to figure out what links them together.

Notes

It looks like the sick people stayed in different hotels, ate in different restaurants, and visited different tourist sites.

Since you don't even know what the illness is or how it's spread, you make a list of questions to ask the sick people and their families, asking things like:

• When did you first get sick?
• Where did you stay overnight?
• Did you visit any of the following: the Liberty Bell, Independence Hall, the Museum of Art, the military conference?
• Where did you eat? What did you order? Did you take a bite of anyone else's food? Did you have any condiments (mustard, ketchup, mayonnaise, tartar sauce) on the side?
• Did you drink water or a soda? Did it have ice in it?
• Is anyone else in your family sick?

Clue 3

You need to talk to as many people who were at the conference as possible.

Panic is spreading across the country. Major magazines are putting the outbreak on their covers!

You've learned that many of the sick had stayed at the Deluxe Hotel, but, strangely, only one of the hotel's 400 workers got sick.

Your best lead is the military conference, which was actually held at that same hotel. You need to figure out exactly what the sick people did at the conference, which is going to take some detective work. The conference was 4 days long, and people went to different events on different days.

Data

Tip: To identify the likely source of the outbreak, look for a high attack rate among those who attended a specific event and a low attack rate among those who did not attend it.

You also need to talk to people who went to the conference but aren't sick. This is harder than it sounds, since no one at the conference kept an attendance list. You and a team of EIS officers have to call veterans' groups all over the state, trying to track people down. After a few days of work, you finally get information on 400 healthy people and 200 sick people.

You need to ask each sick person which events they attended at the conference and calculate the "attack rate" for each event.

Clue 4

All of the sick were in Philadelphia some time between July 21-24.

One bit of good news: you haven't turned up any evidence that sick people have spread the illness to anyone else. So at least it doesn't seem to be contagious.

But you still have a lot of unanswered questions. One hotel guest, an airline pilot, got sick even though he was only there for a few hours, taking a nap between flights. A local taxi cab driver who never even entered the building is also sick.

In fact, there are a surprising number of people with the same illness who did not go to the conference but were in the city during those same days. You go back and talk again to these people, and this time you specifically ask about the Deluxe Hotel.

Cases

Some of the sick never even entered the hotel.

You find out that all of these people had gone into or at least passed by the Deluxe Hotel on the days of the conference.

Some of them say they went into the hotel to get a drink to cool off from the heat. Others stood near the entrance, where they could rest in the shade and feel the air conditioning. Some only walked on the opposite side of the street, yet they still got sick!

Whatever bacteria or virus you're facing is incredibly powerful. One man tells you that his wife went into the hotel just to use the bathroom. She was there less than 20 minutes, yet she died days later!

Clue 5

Your team has discovered a new bacterium.

Weeks and then months go by, and despite all the hard work from you and so many others, you still don't know what caused the outbreak. You don't even know what the illness was! The unsolved mystery drives you crazy.

Then you finally get a break. Working late one night in December (nearly 6 months after the outbreak started) a laboratory scientist on your team reruns some new tests. He sees something he'd missed before: it looks like a new type of bacterium! He and others on the team look through more samples from the sick and see that the unfamiliar bacterium is present in many of these samples, too.

Cases

This shows a Legionella pneumophila (Legionnaires' disease) bacterium as seen through a scanning electron micrograph (SEM). Scientists digitally added color to this image so that the bacteria would be seen more clearly.

More research shows that the new bacterium causes an infection of the lungs, a form of pneumonia. Early symptoms of the illness are much like the flu. After a short time (in many cases, a day or two), more severe pneumonia-like symptoms appear. If it isn't treated with the right kind of antibiotics right away, it can kill.

As a result of your discovery, you look at 2 other unsolved outbreaks from recent years and learn that this bacterium was present in those cases, too. You've actually solved 3 outbreaks with one discovery!

Definition

This shows a Legionella pneumophila (Legionnaires' disease) bacterium as seen through a scanning electron micrograph (SEM). Scientists digitally added color to this image so that the bacteria would be seen more clearly.

Your team names the new bacterium Legionella, and the disease Legionnaires' disease, after the American Legion conference where the outbreak started.

Additional research shows that Legionella bacteria are found naturally in the environment and grow best in warm water, like the kind found in hot tubs, hot water tanks, cooling towers that air condition large buildings, plumbing systems, and fountains.

People get Legionnaires' disease when they breathe in a mist or vapor (small droplets of water in the air) that has been contaminated with the bacteria. Antibiotics can cure most cases, but some people can die even if they do receive treatment.

Clue 1

Cindy is in serious condition and is struggling to breathe.

A 7-year-old girl named Cindy has been in serious condition since May 16 with a high fever, headache, swollen glands, and a rash. The rash looks similar to chickenpox with large swollen spots all over the body.

Doctors have run tests for different illnesses like MRSA (Methicillin-resistant Staphylococcus aureus), herpes, or a fungus. The results won't be back for a day or so, but a few doctors actually think the rash looks like smallpox, a deadly disease that was wiped out a few decades ago.

Fears are rising as doctors can't agree and calls are coming in about similar rashes across the state.

Cases

Everyone who is sick is experiencing extremely high fevers, chills, rash, and a sore throat.

Four new cases have been reported. The most common symptoms are:

• Very high fever
• Rash
• Chills
• Sore throat
• Swollen glands

Some people also have nausea or diarrhea.

The cases are spread across the state. Most of those who have become sick don't know each other, except for one household where 2 people are sick. No one is sure how the illness is spreading.

Definition

Smallpox smear under high magnification.

What is Smallpox?

Smallpox is a serious, contagious, and sometimes fatal disease. Infected persons get high fevers and raised bumps on their face and body.

Smallpox has been around for thousands of years, but a successful vaccination program finally ended the disease (the last naturally occurring case was in 1977).

After the terrorist attacks on September 11, 2001, however, governments are concerned that terrorists might find a way to use smallpox as a weapon. For this reason, the US government has stockpiled vaccine and an antiviral for smallpox treatment.

Clue 2

So far, all of the tests have come back negative. Doctors are stumped.

The good news is that the tests that doctors ran came back negative for chickenpox and other expected illnesses. Doctors are concerned, however, that the rash might be a rare disease and are worried about how quickly it's progressing.

Seven new cases have been reported for a total of 11 people who are sick.

There's no time to waste! You immediately contact the people who are sick and their families to find out what's causing this outbreak.

Data

Investigators are looking for trends to figure out what the sick have in common.

You've never seen anything like this in Wisconsin before! It's your job to figure out what the mysterious, rare disease is.

You ask the sick people what they've done lately, and interestingly enough, you learn that 2 of the sick just returned from a trip to Costa Rica. They tell you that while on vacation they took a tour of the rainforests and came into contact with several rare and exotic plants and animals.

Most of the people didn't have any serious health problems before this and haven't had any contact with the other sick people. You're still struggling to find the connection between all of these cases.

Clue 3

Cindy is now in intensive care. There are a total of 6 people hospitalized.

You need to act fast! Cindy, the 7-year-old girl, has been in intensive care for several days and is now on a breathing tube because her throat is so inflamed. There are a total of 6 people in the hospital now, 4 of whom are in critical condition.

What's worse, 3 new cases have just been reported. And the scary thing is, there may be more cases out there. Since the disease starts out fairly mild with fever, headache, muscle aches, and exhaustion, there's no telling how many others may be sick, as the rash doesn't appear until 1-3 days after the fever.

Cases

One of the people who just developed the rash works at a local pet store.

In talking with the 3 new people who are sick, you learn that one of them works at a local pet store, which only makes you more suspicious. Now, you really start to consider that the disease is zoonotic (a disease that can be spread from animals to humans).

You decide to get more information about the types of animals the sick people have come into contact with. During your interviews, many of the sick talk very affectionately about their pets and how they interact with them. This interaction includes kissing, cuddling, and often letting them sleep in their beds.

In the back of your mind, you're still not sure the animals are to blame as there are 2 sick people who haven't had any contact with animals. However, it's the best lead you've got, so you need to follow-up on it.

Data

You ask the people who are sick about the types of animals they have come into contact with.

Of the 14 who are now sick, 12 have been in contact with animals. Many of the sick people have several pets, and others live on farms with many different kinds of livestock.

The couple who vacationed in Costa Rica also came into contact with a vast number of exotic animals (such as red-eyed tree frogs, black iguanas, and howler monkeys) during their trip.

However, you rule out these exotic creatures since the couple hasn't had contact with any of the others who are sick.

Clue 4

You suspect that the prairie dogs are to blame for the outbreak.

You're on a mission to learn more about these pesky prairie dogs. You start by calling Cindy's parents who tell you that they bought the pet at a local flea market on May 1 as a birthday present for Cindy. She named the little guy Scooter and used to play with him every day, until he got sick and died a few weeks later.

Cindy's mom also mentions that Scooter scratched Cindy during her birthday party on May 4, as she distinctly remembers her daughter crying and asking for a bandage.

You have a solid lead! Immediately, you call the rest of the people who are sick.

Cases

Transmission Electron Micrograph of mpox virus under high magnification.

In talking to the other families, you discover that everyone, except 2 of the patients, had purchased a pet prairie dog in the last few weeks and that many of the pets seemed sick, almost from the very beginning.

While 2 of the patients didn't come into contact with a prairie dog, their grandson (who is also sick) recently had gotten one as a pet.

One of the families allows you to run tests on their prairie dog. The results tell you that the pets are sick with a disease that's never been found before in the US: mpox.

Data

Shipments of prairie dogs in the last several weeks.

You have a mystery on your hands. You need to find out how the prairie dogs got a disease that's usually found in Africa.

You track one of the prairie dogs with mpox back to a local pet store. The owner of the pet shop tells you he purchased several prairie dogs over the last few weeks and gives you the name of the distributor.

The distributor reports that he's made at least 3 deliveries across the entire state in the last month. It's your job to figure out which shipment brought disease into Wisconsin.

Definition

Transmission Electron Micrograph of mpox virus under high magnification.

What is Mpox?

Mpox is a rare viral disease found mostly in Africa. It's typically spread by infected animals that bite or scratch others and can also be spread from person to person through long periods of face-to-face contact.

Symptoms usually appear about 12 days after someone is exposed to the virus. Initial symptoms include fever, headache, muscle aches, and backaches. A few days after the fever appears (approximately 1-3 days), a rash with raised bumps with fluid appears. The illness can be very serious and may last up to 2-4 weeks.

Clue 5

Giant Gambian rats are thought to have been responsible for other mpox outbreaks. This image is of an Epidemic Intelligence Service (EIS) officer investigating an outbreak of mpox in Africa in 1996-1997.

In order to prevent others from getting sick, you need to track down all of the animals that traveled with the prairie dogs to see if other animals are sick as well.

After much work, you're able to find each of the animals. Interestingly enough, you find that one of the Gambian giant rats from the shipment on April 23 died a few days after it arrived at the pet store.

Since the Gambian giant rats were imported from Ghana, you suspect that they may have infected the prairie dogs during the transport. But, there's no way to know for sure until you track the Gambian giant rats back to Africa.

Data

Results of the testing of the animals that traveled from Ghana to the US.

In tracking the Gambian giant rats, you find that there were 6 different types of animals on the flight from Africa in early April.

Once again, you find yourself tracking down exotic animals, but this time they are spread all over the country. You're able to find many still in pet stores, but others have been sold to families or have died.

You order lab work to look for mpox virus in the tissues of animals you're lucky enough to find.

Clue 1

No one can tell where the illness has come from.

It started when a 9-year-old boy was taken to his doctor. He'd been sick 2 days with a fever of 103 degrees, a cough, headache, and chills. The doctor said it was a bad virus and sent him home to get some rest, take medicine for the fever, and drink lots of fluids. He returned to his doctor the next day with nausea and stomach pain, and was again sent home.

After another 3 days, his doctor checked him in to the hospital with a fever of 106 degrees and trouble breathing. He died hours later. The local department of health calls you after learning that several other people in the same county have similar symptoms.

Cases

More information about the sick people.

According to medical records from the local department of health, of the 25 people who are sick or who died:

• 10 are age 12 and younger.
• 6 are ages 13-19.
• 6 are ages 20-59.
• 3 are 60 and older.

And the sick people are reporting the following symptoms:

• 25 (100%) high fever.
• 22 (88%) chills.
• 21 (84%) headache.
• 13 (52%) muscle aches.
• 10 (40%) rash.
• 3 (12%) nausea or diarrhea.
• 2 (8%) confusion.
• 2 (8%) abdominal pain.

Clue 2

Three more people have checked into the hospital.

Seven days after the first person got sick, 3 more people have checked into the hospital, and a second person has died.

You arrive in the county and start your interviews with the people who are sick, which helps you get detailed information about them: what they do for a living, where they've traveled lately, whether they have pets, and more.

Data

What you learned from your interviews.

Twenty-five sick people or their family members were interviewed. Of the sick people:

• 20 (80%) have a pet dog or cat that spends time outdoors.
• 12 (48%) regularly play outdoors.
• 6 (24%) work outdoors as landscapers, construction workers, or laborers.
• 5 (20%) have a sick family member.
• 4 (16%) have other health conditions.
• 3 (12%) returned from a trip to Asia in the last week.

Clue 3

Many of the children are getting a rash.

It turns out that all of the people who are sick either work outdoors, spend a lot of time outside, or have pets that roam around outdoors. Also, all of them live near woods bordering the desert. This suggests that the culprit lurks somewhere in the dry desert landscape - but what is it?

More people are being hospitalized, and more are developing a rash, particularly the sick children. Unlike chicken pox, this rash isn't itchy. And the patients are a lot sicker than they'd be with chicken pox. You need to hurry!

Cases

You make an attack rate chart based on your interviews.

Doctors run a number of tests, which the health department sends to a special lab at the Centers for Disease Control and Prevention (CDC). While you wait for the results, you take a closer look at your interview data to see what the sick people have been doing outdoors.

The data shows that a lot of people have used the swimming pool. And when you visit some of the patients' houses, you notice that some of their pet dogs have ticks.

Data

You make an attack rate chart based on your interviews.

You interview 100 people. Twenty-five of them are sick. The others are not sick, but they participated in the same activities as those that are sick. In outbreak investigations we call these people "controls."

Each person was asked what they did before getting sick. The "attack rate" was calculated for each activity.

Hint: To find a possible source of the outbreak, look for both a high attack rate for those who participated in an activity and a low attack rate among those who did not participate.

Clue 4

Rickettsia rickettsii bacteria, which causes RMSF.

Rashes have become more common with patients who have been sick for a few days, especially the kids. That, combined with test results that have come in from CDC, point to a new diagnosis: Rocky Mountain spotted fever (RMSF). Your first step is to put all of the patients on a special antibiotic that can cure RMSF.

RMSF is spread by bites from infected ticks. One of the things that makes RMSF so dangerous is the fact that its early symptoms are so similar to a bad virus, tricking doctors. This is particularly bad because untreated RMSF can be fatal.

Still, there are 2 things that bother you. For starters, only 10 out of 25 (40%) of the patients said they'd been bitten by ticks. And second, RMSF has never been reported in this state before.

Definition

Brown dog tick.

What is Rocky Mountain spotted fever (RMSF)?

RMSF is caused by the bacterium Rickettsia rickettsii and is spread to people who are bitten by infected ticks. Don't be fooled by its name: this disease has struck people who live hundreds of miles from the Rocky Mountains. Typical symptoms include:

• Fever
• Headache
• Stomach pain
• Vomiting
• Muscle pain
• Rash, which often occurs 2-5 days after fever begins.

RMSF can be severe or even deadly if not treated in the first few days of symptoms. The recommended first line treatment for adults and children of all ages is doxycycline, a special antibiotic that's most effective if started before the fifth day of symptoms.

Health Tips

Guard against ticks when playing outdoors.

In much of the country, ticks are more likely to bite people and pets in warmer months (April-September). But in warmer parts of the country, they can be a problem year-round. You can protect yourself by:

• Avoiding contact with ticks. Stay out of wooded and bushy areas with high grass and leaves on the ground. Walk in the center of trails.
• Repelling ticks. On skin not covered by clothes, use insect repellents that contain 20% or more DEET (Diethyl-meta-toluamide, the best insect repellent). You should also treat clothing and gear (such as boots and tents) with special products to prevent ticks.
• Finding and removing ticks from your body. Bathe or shower as soon as possible after coming indoors, and use a mirror to do a full-body tick check. If you see a tick, remove it with fine-tipped tweezers by grasping the tick as close to your skin's surface as possible. Pull upward with steady, even pressure - don't twist or jerk. Clean your wound with iodine, rubbing alcohol, or soap and water.
• Check your pets, coats, and day packs. Put clothes in a dryer on high heat for an hour to kill remaining ticks.

Clue 5

Dogs can bring ticks into the house.

Tests reveal that this outbreak of Rocky Mountain spotted fever has been spread by the brown dog tick (Rhipicephalus sanguineus). This is the first time the brown dog tick has been found to carry RMSF.

Worse, this tick is commonly found across much of the US, and it feeds mostly on dogs.

That means dog owners in other parts of the county could be at risk if the disease spreads to new areas.

The best strategy for protecting residents from RMSF is by keeping brown dog ticks off of dogs and out of people's yards. But what's the best way to do this?

Health Tips

Check you pets for ticks daily.

Dogs can easily be bitten by ticks and bring them into your home. Dogs can also get RMSF and die from the disease, just like people. And there's no vaccine to prevent RMSF. The best way to protect your family and your pet is by giving your dog a special collar or other product that prevents ticks.

To reduce the chances that a tick will pass disease to you or your pets:

• Regularly use a collar or other treatment that prevents your dog from getting ticks.
• Check your pets for ticks daily, especially after they spend time outdoors.
• If you find a tick on your dog, remove it right away with tweezers or your gloved hand.
• Ask your veterinarian to do a tick check at each exam.
• Talk to your vet about diseases spread by ticks in your area and ways to prevent them.
• Keep your lawn mown, and cut back at tall weeds so ticks don't have a place to settle.

Clue 1

Ice cream served at the party.

The health department gets a report that five children who attended the party have been admitted to a local hospital with severe diarrhea. The next day, a parent calls the local health department to report that her four kids (who all attended the same birthday party) also have severe diarrhea. CDC's team of Epidemic Intelligence Service (EIS) officers, known as "Disease Detectives," is called in to help investigate.

The lead EIS officer asks you to interview the parents of the children. One mother tells you that she heard that the homemade ice cream served at the party had been made with raw eggs, and she suspects foodborne illness.

Tip

Food and drinks served at the party.

If you suspect foodborne illness that is linked to an event (for example, a birthday party) focus on foods that the patients have in common. But keep an open mind about other possible outbreak sources, such as drinks.

Even though foodborne illness might be suspected, there might be other things that are to blame for the outbreak.

Clue 2

Kids opening birthday presents.

After talking to the family who hosted the birthday party, you learn that about 30 kids and 16 adults attended the party on Sunday, August 1, at the Community Swim Club.

After the guests arrived, most of the kids played games and swam in the activity pool. After all of the games and swimming, the guests ate cake and ice cream.

The party hosts state that the ice cream was not made with raw eggs. In fact, 2 children who are sick left the party before the food was served. So, you decide to interview all who attended the party.

Clue 3

A view through the microscope of Crypto in feces (poop).

Your investigation skills pay off! After talking with the kids and parents, you discover that the patients did not eat the same foods and quickly rule out foodborne illness.

Test results for 9 sick kids who attended the party came back positive for Cryptosporidium (or "Crypto"). The health department puts out an alert to encourage testing for Crypto (since it's not routinely done in most laboratories). Soon after, a local hospital reports 13 new Crypto infections in patients who did not attend the birthday party.

Definition

A view through the microscope of Crypto in feces (poop).

What is Cryptosporidium (or "Crypto")?

Crypto is a parasite that can cause watery diarrhea (that lasts a week or more), stomach cramps or pain, vomiting, and tiredness. Crypto is easily spread between people and from animals to people. You can get Crypto by:

• Coming into contact with feces (poop) of a person or animal infected with Crypto and then touching your mouth.
• Eating uncooked foods contaminated with (containing) Crypto.
• Swallowing water contaminated with Crypto.

Symptoms usually begin within a week of infection and can last a week or more in people with healthy immune systems. Learn how to protect yourself from getting sick.

Health Tips

When washing hands, wet hands, apply soap, rub hands together for at least 20 seconds, and rinse under running water. Dry with a clean towel or air dry.

Kids and adults can take steps to help protect themselves and others from Crypto and other germs:

• Practice good handwashing, especially before eating, after using the toilet, changing diapers or helping someone use the toilet, and handling an animal or animal waste.
• Don't swim when you have diarrhea. You can spread germs in the water and make other people sick.
• Don't take kids sick with diarrhea to child care facilities until the diarrhea has stopped. This will help protect other kids and staff.

Clue 4

Kids playing at the Community Swim Club.

After talking with several of the new patients, you discover that they all swam in the Community Swim Club's activity pool on the weekend of July 31-August 1.

In reviewing the data, you learn that most of the individuals got sick within 1 week of swimming in the activity pool. Data about each of the known cases were collected, including:

• Age
• Gender
• Date and time of swimming in the activity pool.

Data

Disease Detectives use epi curves to study how many people become sick each day. Epi curves are updated as new data are gathered.

So far, you have learned that:

• 22 people are sick.
• 5 people have been hospitalized.
• Most patients became sick within 1 week of swimming in the Community Swim Club's activity pool.

Learn more about an epidemic curve (epi curve).

Cases

Data about each of the 22 people who are sick.

Data about each of the known cases were collected.

The data showed that many of the people who are sick were in the activity pool on the morning of Saturday, July 31, for an infant-parent swim class. Others were in the activity pool during the birthday party on the afternoon of Sunday, August 1.

Definition

Disease Detectives use epi curves to study how many people become sick each day. Epi curves are updated as new data are gathered.

What's an epidemic curve (epi curve)?

An epi curve shows how an outbreak changes over time. It includes:

• Date when each person became sick
• Number of people who became sick on each day

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

Learn how to read an epi curve.

Clue 5

The swim club has 2 locker rooms, an activity pool and a lap pool. The activity pool was used for both the infant-mother swim class and the birthday party.

The source of the outbreak is likely the swim club, so you request the attendance records for the weekend of interest.

Data

This chart includes the attack rates of some of the activities people participated in at the club.

During the interviews, you ask each person what they did at the swim club during their visit and ask one of the EIS officers to calculate the "attack rate" for each activity.

Based on the interviews, the following attack rates were calculated:

• Used the locker rooms: 24%
• Used shower facilities: 29%
• Went into the activity pool: 58%
• Ate while at the pool: 59%
• Swallowed water while in the activity pool: 98%

Hint: To identify the likely source of the outbreak, look for a high attack rate among those who participated in a specific activity and low attack rate among those who did not participate.

Tip

Parents and kids at the infant-parent swim class.

During the interviews, several parents report that the diaper of one of the infants leaked diarrhea into the activity pool water during the infant-parent swim class. When you review pool records for the day of this class, you find that the pool did not receive any extra chlorine treatment after the diaper leaked.

Most germs are killed by chlorine within minutes, but Crypto can survive for days even in a pool with proper chlorine levels. To kill Crypto in a pool, the pool must be closed to swimmers and the chlorine levels must be raised to high levels for hours. This is why it's important to keep germs out of the water in the first place.

Clue 1

Hundreds of villagers are sick.

A Kenyan health worker reports that the villagers are in a panic. More than 400 people in the North Eastern Province have flu-like symptoms. Most of the sick are complaining of fever, muscle pain, weakness, and dizziness.

Although many of the sick felt better within the week, more than 100 were hospitalized due to extremely high fevers, blindness, and seizures. Some have slipped into a coma and some have bled to death.

Data

Disease Detectives use epi curves to study how many people become sick each day. Epi curves are updated as new information is gathered.

During your talk with the health worker, you learn that most of the cases are quite mild, while others are more severe.

In reviewing the data, you find that most of the individuals got sick from December 15 - 30, but recovered quickly (within the week).

Learn more about an epidemic curve (epi curve). Find more detailed information on how to read an epi curve.

Definition

Disease Detectives use epi curves to study how many people become sick each day. Epi curves are updated as new information is gathered.

What's an epidemic curve (epi curve)?

An epi curve shows how an outbreak changes over time. It includes:

• Date when each person became sick
• Number of people who became sick on each day

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

Learn how to read an epi curve.

Clue 2

Many sheep are showing signs of sickness.

The health worker walks through heavy mud for many miles to identify the sick and interview them about their experience.

After reviewing the data from the interviews, you discover that many of the sick are herdsmen, farmers, and housewives. The interviews also reveal that thousands of the villages' sheep have died. Many more sheep are starting to show signs of sickness.

Cases

The chart shows the percentage of people who are sick and the activities they participated in.

You have found that many of the people who are sick have been in contact with some of the sick animals. In fact, of those who are sick:

• 75% reported handling raw meat or raw milk.
• 67% reported having contact with a sick animal.
• 25% reported slaughtering animals.
• 10% reported having contact with a sick person.

Clue 3

The herdsmen have reported seeing swarms of insects near the sheep.

• Many of the sheep live near the flooded river and eat grain from the nearby fields.
• Herdsmen have reported seeing swarms of insects around the sheep.
• The local veterinarian noticed intestinal parasites (worms that live in the intestines) in 10 of the sheep.

Data

This chart includes the attack rates of the activities people participated in prior to becoming sick.

More than 1,000 villagers were interviewed, those who were sick as well as those who were healthy. Each person was asked what they did one week before getting sick. One of the health workers calculated the "attack rate" of each item.

Based on the interviews, attack rates were calculated for those who participated in the following activities:

• Drank water from flooded streams: 9%
• Bitten by a mosquito: 83%
• Have been around sheep: 70%

Hint: To find a possible source of the outbreak, look for both a high attack rate for those who participated in an activity and a low attack rate among those who did not participate.

Clue 4

Mosquitoes can spread infections by biting humans or animals.

The mosquitoes are getting worse. You have noticed insect bites on the sick sheep as well as on the people who are ill.

Since you suspect mosquitoes play a role in how the disease is being spread, you decide to test the sick for two diseases that cause similar symptoms in humans: yellow fever and Rift Valley fever (RVF).

Definition

This electron micrograph shows the yellow fever virus at high magnification.

Yellow fever or Rift Valley fever (RVF)?

Both diseases are spread to humans by mosquito bites. The most common symptoms of both yellow fever and Rift Valley fever include:

• Fever
• Weakness
• Back pain

While yellow fever primarily affects humans, Rift Valley fever may affect both animals and humans. RVF can also be spread by exposure to blood, body fluids, or tissues of infected animals. Outbreaks usually happen during years of very heavy rainfall and flooding.

Learn how to protect yourself from getting sick.

Health Tips

Mosquitoes often carry viruses.

The best way to prevent yellow fever or Rift Valley fever (RVF) is to:

• Avoid mosquitoes.
• Use an effective insect repellent on visible skin and clothing.
• Wear long-sleeves, long pants, and socks when outdoors.
• Stay in buildings with screened or air-conditioned rooms.
• Use bed nets or mosquito netting around beds.
• Avoid exposure to blood or tissues of animals to prevent Rift Valley fever.

Clue 5

Using nets over a bed can give protection from mosquitoes.

The blood test results are in. It looks like Rift Valley fever is to blame.

In your talks with the locals, you've uncovered a few key findings that may help uncover how the outbreak spread:

• Not all of those who were ill had contact with sheep.
• Many of the villagers reported having old or damaged mosquito nets.
• All of the villages in the area experienced heavy flooding during the recent rainstorms.

Definition

This electron micrograph shows a tissue that has been infected with the Rift Valley fever (RVF) virus at high magnification.

What is Rift Valley fever?

Rift Valley fever (RVF) is a disease caused by a virus that affects several species of domestic animals and humans. Both humans and animals get Rift Valley fever from the bite of an infected mosquito. Humans may also get Rift Valley fever by exposure to blood, body fluids, or tissues of infected animals. Outbreaks typically happen during years of unusually heavy rainfall and flooding.

The most common symptoms include:

• Fever
• Weakness
• Back pain
• Dizziness

Most people who have Rift Valley fever get better within two days to one week, but some can die from more serious complications.

Clue 1

Students eating pizza.

A couple of students are feeling miserable after a late night of partying and eating pizza following a big win by the university's football team.

Two students called the student health center asking for an official excuse to skip midterm exams. The nurse at the health center didn't think much of this until more students started showing up with vomiting and diarrhea. Dozens of students are sick and staff at the health center suspect that a stomach bug might be going around.

Cases

Sick college student.

Within the last 2 days, 53 students have come to the student health center with similar symptoms, all of which began suddenly. Of the 53 students:

• 91% are vomiting.
• 87% have nausea.
• 72% have diarrhea.
• 67% have stomach cramps.
• 61% have a fever.
• 53% have a headache.

The medical staff tells you that they have diagnosed the students with acute gastroenteritis. However, the routine tests at the student health center did not identify the cause.

Definition

Student with nausea, vomiting, and stomach cramps.

What is Gastroenteritis?

Gastroenteritis is an inflammation of the stomach and intestines. The most common symptoms include:

• Watery diarrhea
• Vomiting
• Headache
• Fever
• Stomach cramps

The symptoms typically last for 1 to 3 days. Although viruses are the most frequent cause, gastroenteritis can also be caused by bacteria, parasites, or chemicals.

Clue 2

Student with stomach cramps.

Things are getting worse. Since the beginning of the week, 76 students have visited the student health center with similar symptoms. Most of the students are getting better in a day or two. But 3 students have become dehydrated and are being treated in a local hospital.

The student health center collected stool samples from the sick students and performed bacterial testing. The results came back negative for the common bacteria and parasites that could have made the students sick. So, the samples were sent to the health department laboratory for viral testing.

Data

Epidemic curve showing when the 76 students experienced their first symptoms. A sick person was defined as students experiencing vomiting or diarrhea, nausea, and stomach cramps between March 9th and 12th.

To find out what caused the outbreak, you need to know when it started. After talking with the staff at the student health center, you find out that:

• March 9: First students got sick.
• March 10: The number of new patients peaks.
• March 12: Symptoms began for the last people who got sick.

Symptoms from a typical stomach bug usually start 1 to 2 days after coming into contact with the virus. Based on the data, you suspect that the first person was exposed around March 8 and that the "exposure period" (the time when the students were likely exposed to the contamination) is March 7-10.

View the epidemic curve (epi curve) to see when the outbreak started. Learn more about an epi curve.

Health Tips

Student drinking water.

The best ways to stay hydrated when you have gastrointestinal illness are to:

• Drink plenty of clear liquids (water, broth, or sports drinks).
• Avoid alcohol or drinks with caffeine (colas, teas, and coffee).
• Eat ice chips or frozen ice pops.
• Use a squeeze bottle or a straw if you are too weak to drink from a cup.

Definition

Epidemic curve showing when the 76 students experienced their first symptoms. A sick person was defined as students experiencing vomiting or diarrhea, nausea, and stomach cramps between March 9th and 12th.

What's an epidemic curve (epi curve)?

An epi curve shows how an outbreak changes over time. It includes:

• Date when each person became sick.
• Number of people who became sick on each day.

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

Learn how to read an epi curve.

Clue 3

Students studying on campus.

Great news! The outbreak seems to be slowing down. No other students have gotten sick in the last 3 days. Those who are sick are beginning to feel better.

In the meantime, you've been trying to find out what caused the outbreak by interviewing the students and have learned some important information. Now, you need to look for patterns in the data to find the source of the outbreak and stop further spread of the illness.

Cases

Data from the 76 students who are sick.

In looking over the students' school records, you find that the 76 sick students have some things in common for the time when they were most likely exposed to the contamination (March 7-10):

• All the students live on campus in one of the university's 4 dorms.
• All drank municipal tap water from the dorms.
• All ate in the school's food court, which is 1 of 3 cafeterias on campus.
• Only a handful of the sick students have classes in the same buildings.

Clue 4

Sandwich from the food court.

While you suspect the outbreak started at the food court, you need to confirm your suspicions. So, you decide to interview other students from campus who are not sick ("controls").

You're able to talk with 273 students who don't have any symptoms. You discover that most of these students did not eat at the food court during March 7-10 and instead chose to eat at one of the other cafeterias on campus. However, 100 of the students who are not sick did eat at the food court during this time.

In order to identify why some students got sick and others did not, you need to identify the source of the exposure. So, you ask the students about the foods they ate at the food court and also interview the staff who work in the food court.

Cases

The salad bar at the food court.

Of the 76 students who are sick, you were able to interview 62 students. You were also able to interview the 100 students who ate at the food court between March 7-10 but did not get sick ("controls"). You ask all of the students to list the foods they ate at the food court during the days in question.

Take a look at the data to figure out which foods are causing students to get sick.

Data

Attack rates based on the interviews with the students who got sick and the students who did not get sick ("controls").

You use the data from the interviews to calculate the "attack rate" for each of the foods eaten at the food court during March 7-10.

Interestingly, you discover that most of the students who are sick ate sandwiches, while the students who are well tended to eat foods from the salad bar, the grill, the soup line, or the pizza counter. So, you calculate the attack rate of the foods from the sandwich line to find out what is causing students to get sick.

Hint: To identify the likely source of the outbreak, look for a high attack rate among those who ate a specific food and low attack rate among those who did not eat this food.

Tip

Food court worker making sandwiches.

You also interview the workers in the food court. Helen, the person in charge of making sandwiches, tells you that she wasn't feeling well and had diarrhea and stomach cramps a few days before the outbreak began.

While you are interviewing her, you notice that she frequently touches other surfaces, including the cash register, and then goes back to handling food without washing her hands. You also notice that there aren't any signs posted about employee handwashing.

Clue 5

Norovirus detected by a transmission electron micrograph (TEM).

The results are in! The health department calls to tell you that the samples from the sick students tested positive for norovirus.

You suspect that the sick food court worker spread the virus when she was sick with diarrhea and handled the foods in the sandwich line.

Learn how you can protect yourself from norovirus.

Definition

Norovirus detected by a transmission electron micrograph (TEM).

What is Norovirus?

Norovirus is very contagious. You can get infected with this virus by:

• Eating foods or drinking liquids contaminated with norovirus.
• Touching objects and surfaces contaminated with norovirus then putting your fingers in your mouth.
• Having close contact with someone who is infected.

The most common symptoms are diarrhea, vomiting, nausea, and stomach pain. Most people who get sick with norovirus feel better within 1 to 3 days.

Learn how to protect yourself from norovirus.

Health Tips

When washing hands, wet hands, apply soap, rub hands together for at least 20 seconds to lather, rinse under running water. Dry with a clean towel or air dry.

The best way to help prevent norovirus infection is to:

• Wash your hands carefully with soap and water.
• Rinse fruits and veggies carefully.
• Cook seafood to proper temperatures.
• When you are sick, do not care for or make food for others.
• Avoid touching ready-to-eat foods with your bare hands.
• Clean and disinfect contaminated surfaces.
• Wash soiled laundry thoroughly.

Clue 1

This map shows the location of Dandano, a village in Guinea.

Village elders don't know what is causing about 30 of the villagers to get sick. Family members are doing their best to care for them.

You need to find out how these people got sick. By tracking their activities, you can narrow down the initial source of the illness. This is a critical step in disease prevention and the start of contact tracing.

Cases

What do the sick people have in common? The table above shows the results of the interviews you conducted with the 30 sick people.

You start by interviewing the 30 sick people to find out what they were doing before becoming ill.

Many villagers work in the nearby fields with livestock or crops. Several others draw water from a well a few miles away. Some travelled outside the village to the closest city for work.

Most of the sick villagers visited the traditional healer. A traditional healer helps treat most minor illnesses and problems. They use knowledge and skills unique to their culture to help treat and prevent illness.

Definition

A disease detective and a member of the local armed forces discuss contact tracing.

Contact tracing is finding everyone who comes in direct contact with a sick person. Doctors then watch those people for symptoms for several days.

If that person starts to show symptoms, there are 3 possible next steps: isolation, testing or additional care. Then the cycle starts again, the new sick person's contacts will be located and watched for days. Contact tracing can be a lot of work, but it is important to help stop the spread of a disease.

Clue 2

After talking with those who saw the traditional healer you learn that he was also sick and later died. You use the dates that people visited the healer to help with your investigation.

There are now 35 people confirmed sick in Dandano and 3 have died. There may be more, but you can't confirm how many because the healer hid the actual numbers of sick people.

Other villages nearby are starting to experience the same problems. You send blood samples of sick people for testing to find out what is causing people to get sick.

Other organizations like the World Health Organization (WHO) and Doctors Without Borders are called in to help fight the disease.

Data

After seeing the healer, what's the longest amount of time before someone got sick?

It's important to find how long it takes for a disease to appear after coming in contact with another sick person. This is called the incubation period. It is calculated by the longest amount of time between when a person is exposed to a disease and when they begin to show symptoms. This information helps medical officers know how long to monitor someone before deciding if they are sick or well.

You gather data on a sample of the sick people who saw the healer. You note how long it took before they started to show symptoms. You find out that most people visited the healer for unrelated reasons like back aches or broken arms. They later started to exhibit similar symptoms.

Clue 3

More people, including medical workers, are starting to get sick. How can you protect these people?

The test results confirm that these villagers have Ebola. In the village of Dandano, 75 more people have gotten sick, and 10 more have died. This brings the total to 110 sick and 13 deaths.

The disease is spreading fast in neighboring villages as well. You need to figure out who the disease affects and if certain people are more prone to getting sick.

At the local missionary clinic, the medical workers who are caring for the sick people are also getting sick themselves. Two nurses are now showing symptoms: fevers, headaches, vomiting, and muscle pains! They have been giving meals, washing, and taking blood samples from sick people. You warn the rest of the staff to be very careful while caring for them. You recommend they wear protective clothing to prevent the spread of the disease.

Definition

Ebola virus from an electron micrograph under high magnification.

What is Ebola?

Ebola is a rare and deadly disease caused by infection with an Ebola virus species. These virus species are found in several African countries. Since its discovery in 1976, Ebola outbreaks have appeared occasionally in Africa and in the Philippines.

The natural host of Ebola remains unknown, but researchers believe the virus starts in animals - most likely bats. Ebola can be spread among people through direct contact with:

• Blood or body fluids like urine, saliva, sweat, poop, or vomit of a person who is sick with or died from Ebola, or
• Objects that a person who is or was sick has touched.

Symptoms of Ebola can include fever, severe headache, muscle pain, weakness, fatigue, diarrhea, vomiting, abdominal (stomach) pain and unexplained hemorrhage (bleeding or bruising).

Data

Data table comparing the attack rates across different groups of people. What trends do you see?

Now that you know the disease is Ebola, you want to find out what groups of people are particularly affected. You need to find out what the people who are sick have in common. This will help you determine if one group is affected more than another.

You note ages, occupations, and gender of people who are sick and compile it into charts. You compare the same information to people who are well, and look for any trends in the data.

A partner organization shares the data they have also collected on attack rates in their regions. You can compare your results to the rest of the country to see if certain regions are particularly affected by the disease.

Notes

Personal protective equipment, or PPE, helps protect medical workers from coming into contact with disease.

In order to minimize contact with people who are sick, healthcare workers begin wearing personal protective equipment (PPE). PPE is specialized clothing or equipment worn for protection against infectious diseases. PPE might include gloves, masks, goggles, boots and protective gowns.

PPE helps by creating a protective barrier between sick person and a healthcare worker. Wearing PPE will help the Guinean healthcare workers provide care to sick people, while protecting themselves from getting sick.

After healthcare workers begin wearing PPE, you notice that fewer healthcare workers are getting sick. The PPE is working!

Clue 4

Families have a tough time in dealing with the spread of Ebola.

The best way to stop the spread of Ebola is to isolate the people who are sick. Once you know this, you can separate people and observe them for symptoms over a 42-day period.

But, you are struggling to identify the people who are sick. Many sick people are saying they are healthy so that friends and family won't ignore them. This is a big problem when conducting contact tracing. It's hard for you to trace who has come in contact with a sick person and who hasn't.

Mothers and fathers are doing their best to stay with, hold, and comfort their sick children. But healthy villagers want to isolate the sick and keep them away by boarding up their homes.

Cases

Dozens of people might attend a single funeral for a sick person. At one funeral, Ebola can spread rapidly from just one event.

You hear that a neighboring village held a funeral for a midwife who passed away last month. Over 100 people attended the funeral; 18 of the people who attended died soon after the funeral. You find out that the midwife had shown symptoms of Ebola before passing away.

Through your investigation you know that Ebola is transmitted through contact with corpses or bodily fluids of an infected person. Many of the traditional burial practices in this area typically involve washing, touching, and kissing the body of the dead. So it's possible that the funeral attendees could have had direct contact with the body and body fluids.

Clue 5

This map shows the regions of Guinea where Ebola has definitely or is likely to spread. But thanks to your work, the spread is slowing down!

You develop some Public Service Announcements (PSAs) to teach people about safe burial practices and other ways to prevent Ebola. Local TV and radio stations are starting to play the PSAs you helped create. A trusted doctor shares this vital information over the airwaves.

The villagers begin to use these practices, which limits the spread of Ebola. Nearby villages and neighboring countries also educate people in their areas to help keep the disease from affecting them. For now, you've contained the spread of Ebola within Guinea. But symptoms don't appear until several days after contact. So it's possible that people are traveling to other parts of the continent without knowing that they could have Ebola.

Notes

This infographic shows the proper way to wash hands to avoid spreading Ebola.

Your public health notices include radio messages, posters, and other informational postings. You are trying to share the facts about Ebola. This includes how it can be transmitted, prevented, treated, where it can be found, symptoms, and other information to help people understand the disease better.

You want to help villagers understand their role in the fight against Ebola. You know that simply sharing this information throughout Guinea can actually save lives. People will become more aware of the risks and avoid actions that could spread Ebola.

Clue 1

Overcrowding, flooding, and the recent deaths of 2 pregnant women and 1 child cause concern among people in the camp. Photo credit: Petterik Wiggers/Panos Pictures.

The population of the Ethiopian refugee camp Jengo has surged to over 100,000 refugees, coinciding with the onset of heavy rains and flooding.

You are working with the United Nations' High Commissioner for Refugees to assess the public health and WASH needs of the population (WASH stands for water, sanitation, and hygiene).

This week, the deaths of 2 pregnant women and 1 child are reported in the camp. Both women were in the third trimester of their pregnancies. It is unknown when their symptoms began, but all 3 patients were reported to have the following symptoms: yellow eyes (jaundice), fever, fatigue, and nausea.

Tip

Pools of standing water harbor mosquitos and germs. Photo credit: Tom Handzel.

Based on your assessment of the camp so far, you know that:

• Heavy rains have led to swarms of mosquitos and standing water surrounding refugees' tents.
• Flooding in the camp has caused the few latrines (a toilet or outhouse, often used by groups in a camp) to flood, contaminating the groundwater supply with feces.

Camp doctors suspect that the deaths are from yellow fever or malaria, which are common illnesses in the region.

When you learn about these deaths, you worry that you don't yet know what this disease is and when it began.

The camp clinic can conduct rapid tests for malaria, but they don't have the equipment or supplies to test for other diseases.

Clue 2

Camp Jengo's clinic is overwhelmed with people of all ages. Doctors are having a hard time managing the high number of patients. Photo credit: Albert González Farran.

Over the next couple of weeks, community health workers identify 8 more patients with yellow eyes. They send the jaundiced patients to the camp clinic, but doctors can't make a final diagnosis. The symptom of jaundice is not unique - patients could have yellow fever, a type of Hepatitis, or even poisoning.

The camp doctors want to know exactly which disease is killing patients so they know which treatments to use, and how to prevent future cases.

Because the camp's lab doesn't have advanced diagnostic tests, blood samples are sent to a specialized laboratory in Nairobi, Kenya for testing. However, it will take weeks to safely transport the samples to the lab and get the test results.

The camp doctors are overwhelmed with people who are sick.

Notes

Refugees collect water from a pond near the camp. Drinking dirty water can cause diarrhea. Photo credit: Tom Handzel.

The clinic is overwhelmed with people of all ages battling watery diarrheal diseases, but most of them do not have jaundice.

Doctors are having a hard time managing the high number of patients with different symptoms.

For now, they are treating all patients by giving them oral rehydration solution, which is water mixed with sugar, salt, and zinc which patients drink to treat dehydration. Sicker patients are hospitalized for IV fluid replacement.

Health Tips

Diarrhea can be treated with oral rehydration solution (clean water, sugar, and salt) and with zinc tablets. Photo credit: Jessica Lucia.

Diarrhea is the passage of 3 or more loose or liquid stools per day. Diarrhea is usually a symptom of a stomach infection, which can be caused by a variety of bacterial, viral, and parasitic organisms.

Infection is spread through contaminated food or drinking water, or from person-to-person because of poor hygiene.

Interventions to prevent diarrheal diseases include safe drinking water, use of improved sanitation, and hand washing with soap; all of which can reduce risk of disease. These types of programs are known as WASH (water, sanitation, and hygiene).

Diarrhea can be treated with oral rehydration solution (clean water, sugar, and salt) and with zinc tablets.

Cases

Characteristics and case descriptions of the 11 patients who have been diagnosed with jaundice during the last 2 weeks.

While you're waiting for the lab to return test results from Nairobi, you have some time to analyze information about the people who have become sick with jaundice.

In the last 2 weeks, 11 patients have been diagnosed with jaundice and 7 have died, but only 4 of the 11 patients have tested positive for malaria. Most of these patients have been experiencing symptoms from 5 - 23 days. 7 patients are female, and 4 are male. The camp clinic also ran rapid tests for Malaria. Now, you are able to see all of the data in one place, so you can look for trends in the data.

Next, you have to ask yourself some tough questions. Do the patients who died have anything in common? Is there any relationship between malaria and this mysterious disease?

Clue 3

To produce reliable results, blood samples must be kept at test-specific temperatures.

Although the camp clinic was able to run rapid tests for Malaria, it sent samples to another lab for more advanced diagnostic tests. After several weeks, you get a phone call from the lab in Nairobi. You're expecting the test results, but you find out the blood samples you sent weren't kept cold enough while they traveled from the refugee camp to the lab in Nairobi. The lab doesn't want to waste its limited resources testing damaged samples - the test results would be meaningless. That means the lab isn't able to tell you what is making patients sick. But the refugees and camp doctors are still relying on you to help them!

You want to act quickly before the outbreak gets much worse. You're not sure exactly what is causing pregnant women with jaundice to die, but health conditions in the refugee camp are poor. Many infectious diseases have related causes. For example, removing mosquitoes prevents both malaria and yellow fever. You don't know what is causing the jaundice, so you decide to focus on preventing diarrheal diseases, which will have a large impact on the whole camp.

Data

Data table comparing access to drinking water, quality of drinking water, access to sanitation, access to hygiene, and prevention knowledge between cases and controls.

Fortunately, community health workers have surveyed almost 400 people in the camp about hygiene and sanitation practices related to the continuing diarrhea outbreak.

The data shows the cases (people who have had diarrhea) are less likely than the controls (people who have not had diarrhea), to use the recommended amount of chlorine to make their water safe to drink. Cases also are less likely to use a latrine, have soap in the home, or know that drinking untreated drinking water can cause diarrhea.

Health Tips

Children fetching water at the refugee camp. Photo credit: journalturk.

Why put chlorine in water?
Adding a safe amount of chlorine to water (about one tablet or capful of watered down solution to about 20 liters of water) and waiting 30 minutes before drinking is proven to reduce most bacteria and viruses. Adding chlorine to water is simpler and costs less than other ways to make drinking water safe.

Clue 4

Camp Jengo educates camp members on the importance of handwashing with soap, using latrines, and drinking treated water. Photo credit: CDC Foundation, David Snyder.

As the conflict in South Sudan continues, a new group of refugees settle in Camp Jengo. This new group has not been exposed to the diseases circulating in the camp, so they don't have immunity. Several weeks pass, and the camp improves water, sanitation, and hygiene conditions by installing handwashing stations, adding latrines, and providing clean drinking water treated with chlorine. Community health workers also conduct small group education sessions on the importance of handwashing with soap, using latrines, and drinking treated water. The number of cases of diarrhea and jaundice begins to fall.

Even though you never figured out what exactly was killing pregnant women, you congratulate yourself on a job well done. Just as you are beginning to feel you have solved the outbreak, a reoccurrence happens. Two months later, several more patients have jaundice again, with more pregnant women dying.

You have no choice but to try again to get lab results. You collect more blood samples, and make sure that they are properly packed so they stay at the right temperature on the 3-day bumpy car ride to Nairobi.

Definition

Immunity means the power to defend yourself from being affected by a disease.

Immunity means the power to keep yourself from being affected by a disease. Exposure to a pathogen (such as a virus or bacteria) triggers the immune system to produce antibodies to a disease. Antibodies are proteins produced by the body that destroy disease-carrying organisms. Antibodies are disease-specific. For example, measles antibody will protect a person who is exposed to measles disease, but will have no effect if he or she is exposed to mumps.

Cases

This epi curve shows that during the first month, cases briefly increase, then taper off as WASH projects are implemented, but 2 months later clusters of cases start to pop up again.

An epi curve shows the number of cases over a 3-month period of time. During the first month, cases briefly increase, then taper off as WASH projects are implemented. But 2 months later, clusters of cases start to pop up again. What has changed in the camp that could explain this?

Clue 5

A little girl from the refugee camp kneels at the edge of a muddy pond for a drink. The pond, formed by heavy rains and runoff is contaminated with Hepatitis E virus.

You finally get the test results from Nairobi - it turns out that patients are dying of Hepatitis E. There is no specific treatment for Hepatitis E, but fortunately the water, sanitation, and hygiene (WASH) projects you started to reduce diarrheal disease also help prevent Hepatitis E. The oral rehydration solution given by doctors is also helpful.

Still, Hepatitis E is hard to control: why else would it return after case counts dropped for months? Water, sanitation, and hygiene actions take time to complete. If any piece of a WASH program is unreliable, (for example, cancelled soap deliveries or a lack of chlorine to make water safe to drink), more people will continue to become infected. The camp managers ask you to write a report with recommendations for controlling Hepatitis E, so you begin by looking at the key risk factors.

Data

Risk factors for cases & controls show adults, 25-54, were more likely to get sick. Also, cases were more likely to have contact with other sick people, take care of animals, or share latrines.

You open your field laptop computer to analyze the data again to see what the cases have in common.

The table shows that adults between 25-54 years old are most likely to be infected. Nearly half of infected cases had contact with another jaundiced person.

Interestingly, many people who drank surface water got sick, and over twice as many people who got sick also took care of animals. Many cases also shared a latrine with 7 or more other households.

Definition

An electron micrograph photo of Hepatitis E viruses (HEV).

Hepatitis E is a liver infection caused by the Hepatitis E virus (HEV). In developing countries HEV infection does not result in chronic Hepatitis E. While rare in the United States, Hepatitis E is common in many parts of the world. It is usually associated with contaminated water supply in countries with poor sanitation. After exposure it may take 2-8 weeks for symptoms to appear, and some people have no symptoms at all. Symptoms of Hepatitis E include:

• Fever, tiredness, not feeling hungry, nausea, vomiting, stomach pain, dark colored pee, clay-colored stools, joint pain, and jaundice (yellowing of the eyes)

While it affects all ages, teens and young adults are most likely to get Hepatitis E.

As you've seen in this outbreak, Hepatitis E can seriously affect pregnant women. There is no commercially available Hepatitis E vaccine, and there is no specific treatment. The sickness usually improves when patients rest and get proper food and hydration.

Clue 1

Renalto is a small town in Arizona near the US-Mexico border.

Karina is a 22-year-old college student who's studying to become a Spanish professor. She commutes from Renalto, a town in Arizona near the US-Mexico border, to Saguaro, Mexico, Monday through Friday to attend the local university, known for its excellent Spanish curriculum.

About 3 weeks ago in late April, Karina had diarrhea and fever for a few days. She recovered and didn't think much of it. In the past few days she's noticed unusual numbness and tingling in her hands and feet. Her legs started feeling heavy, and she's finding it difficult to walk. Then yesterday she was unable to stand up when she got out of bed, and her arms started feeling weak as well. For the past month, Karina has been experiencing back pain. She suspected that it was from all the stress of finals. She visited her doctor a few weeks ago, but her pain didn't go away. In fact, she is feeling worse!

Frightened by these unusual symptoms, Karina rushes to the emergency room. The doctor isn't sure what it is wrong, but he suspects it might be a rare condition called Guillain-Barré syndrome (GBS). He's treated 3 other patients suffering from a similar ailment this week.

If Karina's doctor confirms that she and the others have GBS, this cluster of cases could indicate something even more serious!

Definition

There are 6 new cases. You need to find out how everyone is getting sick and make sure others don't get sick as well.

Guillain-Barré syndrome (GBS) is a rare disorder in which a person's own immune system damages their nerve cells, causing an acute flaccid paralysis, in which people develop weakness in their muscles that worsens over days to a week or so. The affected muscles are limp, and the person has no reflexes when a doctor tests the muscles with a hammer.

GBS can cause symptoms that last for a few weeks to several months. Most people recover fully from GBS, but some people have lasting nerve damage. People sometimes die from problems related to GBS, such as having difficulty breathing when their lung and chest muscles are involved.

Doctors use a series of tests and a patient's history to diagnose a person with GBS. About 1 out of 100,000 people in the United States develops GBS each year. When a person has GBS, they usually have been sick with a different infection first, like a respiratory infection (an infection that affects the lungs) or a gastrointestinal infection (an infection that affects the stomach).

Clue 2

Doctors wonder why so many people have GBS along the border.

Karina's doctor confirms that she has GBS. The local Arizona health department informs you of 8 more people diagnosed with GBS in April and May, bringing the number to 25. All of them live near the US-Mexico border. This is way more cases than is normal in this area!

What is triggering the onset of these cases?

You decide to form an outbreak investigation team made up of state, local, and federal officials to figure out why so many people are getting sick with GBS. First, you interview the sick patients located on the American side of the border in Renalto, Arizona. Next, alongside Mexican disease investigators, you travel to the local hospitals in Saguaro to speak with the GBS patients so you can review medical records of all those who are sick.

Data

In looking at the data, you see that 18 of those sick are from Arizona and 7 are from Mexico. You also notice that everyone who is sick in Mexico recently traveled to the Arizona town of Renalto.

You want to learn more about the people who are sick with GBS, including their symptoms, when they got sick, their recent travel activity, foods they recently ate, and more. It turns out that some patients can't speak with you since they're paralyzed and machines are helping them breathe. Their families help answer questions for them.

After the interviews are completed, you develop a Characteristics and Activities chart. The chart details the responses of the 25 people who are sick, noting the town and country they live in, their age and gender, and which towns they traveled to in the weeks prior to getting GBS.

Several medical records suggest diarrhea, with a few specifically mentioning laboratory-confirmed infections of Campylobacter jejuni.

Definition

This digital image taken through a microscope shows a magnified view of Campylobacter jejuni.

Campylobacter jejuni is a species of bacteria that can cause disease in humans and animals. Many infections are associated with eating raw or undercooked poultry, or from eating food contaminated by raw poultry. These infections are also spread by drinking unpasteurized milk, untreated water, or water that is not treated well enough. These bacteria are not usually spread from one person to another, but this can happen if people drink water or eat food contaminated with diarrhea from an infected person.

Campylobacter jejuni infections are one of the most common causes of illness with diarrhea in the United States. Most cases occur as isolated, sporadic events and not as part of recognized outbreaks. Although illness from Campylobacter jejuni is common, with an estimated 1.3 million infections in the United States each year, most cases are not confirmed by laboratory testing.

People who are sick typically have diarrhea, cramping, stomach pains, and fever within 2-5 days after being exposed. Some infected persons do not have any symptoms. The illness usually lasts about 1 week, and most people recover completely without any specific treatment. Campylobacter jejuni infection can sometimes lead to long-term health problems like arthritis or GBS.

Health Tips

Washing your hands helps prevent disease.

Some simple food-handling practices can help prevent infections of Campylobacter jejuni, such as:

• cooking poultry thoroughly,
• washing hands with soap before preparing food and after handling raw foods of animal origin, and
• not drinking unpasteurized milk or water that is untreated or insufficiently treated.

Clue 3

There are now 24 people who are sick with GBS in Renalto, Arizona, and 7 people who are sick with GBS in Saguaro, Mexico.

Most patients remember being sick with diarrhea before getting GBS, and a few patients tested positive for Campylobacter jejuni infections.

You decide to learn more about what may have caused the stomach illness, particularly since this type of bacteria can trigger GBS.

There is a report of more people who are sick, so you travel to Renalto, Arizona, to see if you can find more clues to help you find the source of the GBS outbreak.

Cases

Guillain-Barré syndrome (GBS) is a rare disorder in which a person's own immune system damages their nerve cells, causing muscle weakness or paralysis.

The number of people who have GBS climbs to 31.

In Renalto, there are 6 new cases, one of them recently diagnosed with a Campylobacter jejuni infection.

So far, based on your investigation, you feel confident that Campylobacter jejuni infections are responsible for the GBS cases for most, if not all, of the patients.

Now you need to find out how they got sick with these bacteria, and make sure other people don't suffer the same fate.

Data

Since vegetables typically aren't associated with Campylobacter jejuni outbreaks, based on the data in the table, which item would you investigate as a possible source of the outbreak?

You interview the 6 new patients in Renalto.

Then, for each of the 31 GBS cases, you try to interview three healthy people who are similar in age and ethnicity to the people who are sick so they can act as controls. You talk to 75 healthy people who serve as controls.

It is important to compare what the people who are sick with GBS ate and drank with what the healthy people (controls) ate and drank, as this can help identify the source of outbreak.

You then calculate and study the odds ratio to see if you can find the source of the outbreak.

Notes

The area in and around Renalto receives very little rainfall, and thus, local farms rely on irrigation water from the Colorado River and from groundwater pumped up by wells.

Renalto is a small city in a rural part of southern Arizona. The biggest industries are tourism related to a national park, agriculture, raising cattle, and the military.

Because the area receives very little rainfall, local farms rely on irrigation water from the Colorado River and from groundwater pumped up by wells.

Definition

Since vegetables typically aren't associated with Campylobacter jejuni outbreaks, based on the data in the table, which item would you investigate as a possible source of the outbreak?

A case-control study is designed to help determine if being exposed to something (food, water, etc.) is related to the people who are sick. To conduct a case-control study, you must follow the steps below.

• First, identify the people who are sick (this is known as the case group or the group known to have the outcome which is the disease or condition being studied).
• Next, identify healthy people who are similar to the people who are sick (this is known as the control group or the group that is free from the outcome).
• Then, interview the 2 groups to learn which people in each group were exposed to different items.
• Lastly, compare the number of times the people in each group were exposed to an item. You are looking to see if the people who were sick (the case group) were exposed more frequently to an item than the healthy people (the control group).

An odds ratio (OR) is a measure of association between an exposure and an outcome. The OR represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring without that exposure. Odds ratios are most commonly used in case-control studies, however they can also be used in other study designs such as cross-sectional and cohort studies (with some modifications and/or assumptions).

Clue 4

While Chicken is a common source of Campylobacter jejuni infections, it does not seem to be the cause of this outbreak.

While investigating whether chicken could be the source of this outbreak, you discover that the people with GBS ate different types of chicken (frozen, fresh, pieces, whole) from various brands sold in big grocery stores on both sides of the border. It turns out that no single store, restaurant, or chain was reported by more than a few patients.

After all this work, chicken doesn't seem to be the source of the outbreak after all! None of the foods that commonly cause Campylobacter jejuni infection seem to be the cause of this outbreak.

But what about water? Both sick and well people drank water in some form (as most people do), and almost all of them had minimal exposure to tap water (for example brushing teeth or showering). Contaminated foods are often distributed far and wide, but contamination of tap water tends to be much more local. Since everyone who is sick spent time in Renalto, Arizona, you decide to investigate the water systems next.

Data

The bacteria testing results from the different water sources are reviewed. Two tests are done: one for coliform levels that identifies a range of bacteria, and another for campylobacter jejuni.

You decide you need to learn more about local water systems. You know just where to start: the environmental health experts.

You and your colleagues meet with water authorities from Saguaro and Renalto, and assemble a team for testing the local water quality.

Together, you review logbooks of water tests from water samples taken from wells, tap water, river water, and irrigation canals in different neighborhoods.

The team also decides to test other sources of drinking water, such as kiosks where people fill large bottles of water.

Clue 5

Authorities need to protect clean local water sources by checking the chlorine levels in the drinking water supply system.

After hours of reviewing your notes, it occurs to you … what if there had been a problem with chlorination of the drinking water?

Even if people didn't drink tap water, they may have used it to rinse off some of their food (like vegetables or fruits that people eat raw without peeling).

You decide to look back at what the patients, like Karina, told you about the fruits and vegetables they ate before getting sick. It turns out that the people who are sick with GBS ate more fruits and vegetables that are typically eaten without cooking than the healthy people in the control group.

People could have been exposed to contaminated tap water even if they didn't drink it. You decide to look back at the possibility of tap water contamination since the water samples tested only represented a single point in time. But you still are not sure how the tap water could be the source of the outbreak since chlorine kills Campylobacter jejuni.

Notes

Engineer checking water in a local water treatment plant.

You and your team decide to talk to local water authorities in Renalto, and learn the city gets its water from shallow groundwater wells. The groundwater has metals in it that discolor the water when chlorine is added.

Unfortunately, some people complained after receiving coffee-colored water coming from their taps, so the operators lowered the chlorine dosage to reduce the discoloration because of the chlorine.

The water authorities also mentioned that a recent earthquake wreaked havoc on part of the irrigation canals of Renalto and ruptured sewage pipes in some neighborhoods. They've been working overtime to fix it.

Next, you decide you need to gather more data about the chlorine levels of the water.

Data

After sampling the chlorine levels at 50 homes in Renalto and checking the chlorine levels every 3 weeks, you find the most of the people who are sick live in an area where chlorine levels were low.

Your environmental health colleagues design an environmental study to help determine if groundwater contamination might have been the problem. The environmental study includes:

• Reviewing chlorine log books and the chlorine levels by date and location,
• Reviewing the source of water for the region and a distribution map, and
• Reviewing any environmental events that may have occurred in the time before the outbreak.

The log book shows chlorine levels at 50 homes in Renalto on May 9th and June 1st. You create maps to show the chlorine levels in different sectors of the city.

On the first sampling, on May 9, you notice lower chlorine levels in the far eastern and western sectors than in the rest of the city. You also see that one of the people who has GBS lives near the eastern area. On the next sampling date, June 1, you see there are more areas that had low levels of chlorine, and that most of the people who have GBS live in areas where the chlorine levels are low.

Clue 1

Dieter has been enjoying the spring weather by reading outside, taking long hikes, and going on bike rides through the countryside.

It's late spring and a 39-year-old history professor named Dieter has been enjoying the spring weather by reading outside, taking long hikes, and going on bike rides through the countryside, zipping past local farms and beautiful scenery.

In early June, Dieter came down with a high fever, headache, and cough. Dieter went to the doctor and was diagnosed with a viral illness and told to go home, drink plenty of fluids, and get some rest. Over the next few days, Dieter's symptoms continued to get worse and he was admitted to a local hospital where he received a chest x-ray and was diagnosed with pneumonia. Dieter was placed on antibiotics, which didn't seem to help make him feel any better. Unfortunately, Dieter is not the only one who is sick.

Notes

Fionna had an extremely high fever for several days before having a miscarriage.

While reviewing Dieter's charts, the hospital doctor notices that Dieter is one of 6 patients admitted to the hospital in the last few weeks. All had similar symptoms and none have improved after receiving antibiotics.

One of the other patients, Fionna, a stay-at-home mom who lives on a small cattle ranch was pregnant when she was admitted. After 5 days with a high fever, Fionna had a miscarriage. Blood tests ruled out the most common infectious causes of miscarriage.

The doctor calls the local department of public health, only to learn that Dieter and Fionna are not the only people who are sick. There is a much larger outbreak happening.

Cases

Reviewing data about the people who are sick can help to paint a picture of what is happening and what the sick have in common.

The local department of public health tells you that there are:

• 19 people that have similar symptoms are sick in the city of Madux, including 6 patients in your own hospital
• 5 people are sick in and around Gallinburg

This brings the total number of people sick to 24. Most of the sick are adults, although there are 3 patients under the age of 19.

The people seem to be of different ages, have different careers, live in different regions, and even have different diagnoses. You need to figure out how these people are connected, what is causing this outbreak, and how the outbreak is spreading.

Data

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

The local health department has begun to collect data on the number of people sick. So far, many people have similar symptoms but the diagnoses are all different.

You decide to chart the date that people first became sick in an Epi Curve to see if you can see a trend in the data.

Definition

Epi curves can help Disease Detectives learn about the spread of an outbreak. Disease Detectives look for a pattern in the curve to see how it is being spread.

An epidemiologic curve, or epi curve, is a tool used by epidemiologists (better known as Disease Detectives), while investigating an outbreak. An epi curve can be used to understand how an outbreak is being spread.

While it is still early, it appears that this outbreak is a point source outbreak. In a point source outbreak, people come into contact with the source of the outbreak for a short time (such as a single event). The number of cases increases rapidly and falls slowly, with most of the cases happening around the same time.

Clue 2

Fionna has been sick for 2 weeks and can't shake off the fever or night sweats.

You're not sure what is causing this outbreak. Fionna has been sick for 2 weeks and can't shake off the fever or night sweats. She is also one of 3 people who are now suffering from photophobia (eye sensitivity to light), pain in muscles and joints, and difficulty sleeping.

You also don't know how the sickness is being spread as there are multiple people in one family who are sick, but in other households only one person in a family is sick. You aren't sure if the illness is contagious.

Since Fionna is one of 6 people sick who live on a farm, you decide to ask all of the sick people what kinds of animals they've come into contact with lately.

Cases

You review the data to see where the people who are sick have things in common. You see that nearly 58% of the sick did not come into contact with an animal.

The local public health department interviews all the people who are sick and finds that while a fair number of people had contact with household pets and farm animals. However, 57.7% of people sick did not have any contact with animals.

During your interviews, you learn that local veterinarian was called out to a local goat farm about a month ago because of an "abortion storm" (an episode in which several pregnant goats miscarry at about the same time). You find that 7.7% of people who are sick had contact with an animal that had recently given birth or had an abortion.

Definition

Zoonotic diseases are diseases which can be passed between animals and humans.

A zoonotic disease can be passed between animals and humans. Zoonotic diseases can be caused by viruses, bacteria, parasites, and fungi. These diseases are very common. Scientists estimate that more than 6 out of every 10 infectious diseases in humans are spread from animals.

People can get zoonotic diseases in many different ways, including:

• Having contact with the saliva, blood, urine, or feces of an infected animal
• Being bitten by a tick or mosquito
• Eating or drinking something unsafe (such as unpasteurized milk, undercooked meat, or unwashed fruits and vegetables that are contaminated with feces from an infected animal)

Clue 3

Many of the local farmers produce milk and cheeses which are sold at the local famer's market.

There are more than 50 cases of sick people and the numbers keep rising every day. You haven't figured out what is making everyone sick or how it is spreading.

Although nearly 58% of the sick haven't had any contact with animals, you decide to follow up on the tip about the goat farm where there was an abortion storm a few weeks ago.

Herman, the owner of the farm, says he has about 1,000 goats which produce goat milk and cheeses which he sells throughout the region, including at the local famer's market. In the last 2 months, 35 pregnant goats on his farm have aborted and Herman says his farm is not the only farm to have a recent abortion storm.

Notes

Q fever is a disease which is typically spread to people from sheep, goats, and cattle.

You ask Herman more about the abortion storm, as this can be a sign of infection with a bacteria called Coxiella burnetii which causes a disease called Q fever.

Sheep, goats, and cattle are the animals which typically spread Q fever to people. The bacteria that causes Q fever are shed in the body fluids, including reproductive materials, of infected animals.

Herman mentions that 3 other local farms have also had recent abortion storms. He also tells you that he and his oldest son had flu-like symptoms about a month ago. They never went to the doctor, and they got better after about a week. The other 4 family members never felt sick. You begin to wonder if their sicknesses could be part of the same outbreak you're investigating.

Definition

Image of a transmission electron micrograph which showed numerous Coxiella burnetii bacteria.

Q Fever, or Coxiella burnetii, the bacterium which causes Q Fever is usually shed in animals' reproductive fluids, milk products, and manure. It is very hardy and can survive in the environment for long periods and can be spread over long distances by the wind.

Many people who get Q fever will never have symptoms; others will get a bad flu-like illness which will eventually fade. A small percentage of people will develop severe symptoms or a chronic infection. Those with heart conditions are most at risk of developing major complications, and women who were infected during a pregnancy are at risk for miscarriages.

Clue 4

Locations of goat and sheep farms and addresses of people who have Q fever.

After testing the goats on Herman's farm and the 3 other farms that recently had abortion storms, you discover the goats on these farms are infected with Coxiella burnetii, the bacterium which causes Q fever. Widespread testing of nearby farms reveals that several farms in the area have goats and sheep with Q fever.

Ninety-five people are sick, but the diagnosis have been different for many people. There are several aspects of Q fever that make it challenging for healthcare providers to diagnose and treat. The symptoms vary from patient to patient and can be difficult to distinguish from other diseases.

The symptoms usually develop within 2-3 weeks of exposure, although as many as half of humans exposed to Coxiella burnetii do not show symptoms.

Notes

Lab tests for Q fever often appear negative in the first 7-10 days of illness. Therefore, healthcare providers must use their judgment to treat patients based on suspicion alone.

When the hospital doctor treating Dieter, Fionna, and several others who have similar symptoms, learns that a local farm has recently had abortion storms, caused by Coxiella burnetii, the doctor suspects that the patients might be suffering from Q fever. He orders test results for each of the patients in his care.

As the first positive results come in, the doctor alerts the local health department who promptly informs other doctors and hospitals in the area. As more and more cases are reported to the local health department, you begin to figure out how this outbreak is spreading.

Health Tips

Treatment is most effective if it is started within the first 3 days. Therefore, physicians should never delay treatment until lab tests confirm Q fever.

An early diagnosis of Q fever must be made solely on a doctor's suspicion. Since Q fever symptoms are similar to many other illnesses, diagnosing Q fever can be challenging and may be missed.

Lab tests often appear negative in the first 7-10 days of illness. Therefore, healthcare providers must use their judgment to treat patients based on suspicion alone.

Healthcare providers may find important information in the patient's history and physical examination which may aid in the diagnosis. Information such as recent travel to rural or agricultural communities where infected livestock may be present is helpful in making a diagnosis.

Treatment is most effective if started within the first 3 days. Therefore, doctors should never delay treatment until lab tests confirm Q fever.

Data

The epi curve above shows the weeks in which people first began to experience symptoms and also shows the strength of the winds during that time.

With 95 people sick with Q fever, you work to figure out what all the people have in common and how the outbreak is spreading. You start by reviewing patients' medical records and interviewing all who are sick.

You learn that most of the people sick are men (60%), aged 40 - 60 years (68%), and that pneumonia was the most common early diagnosis (62%). You also learn that only 3.2% of the patients were working in agriculture and 0.5% in the meat-processing industry. Since there isn't a trend that helps you understand how the outbreak is spreading, you continue your research.

Next, you look at where the goat farms with the abortion storms are located and where the people who got sick live. You notice that many of the sick live within 5 km of an infected farm, but that's still a good distance away. Since you know that Q fever can be spread by the wind, you look at the number of people who got sick each week and overlay the number of days with strong winds in that week. Looking at the data, you notice that during the week where there was a large abortion storm, there were also strong winds. In the 2-3 weeks that followed, there was a large increase in the number of people getting sick.

Clue 5

Number of people sick with Q fever between 2007-2009.

A disease detective's job is never done! Over the course of the next 3 years, dozens of disease detectives worked to control this outbreak. As one of the largest outbreaks of Q fever in history, it's your job to figure what can be done in the future to control and prevent this from happening again.

To do this, you decide to review all sides of this outbreak to better understand what happened and why. In looking at the data, you see that over the last 3 years, 3,525 people got sick from Q fever and 749 people were hospitalized. During this time, abortion waves because of Coxiella burnetii were reported on 28 goat farms and 2 sheep farms. Some goat farms had abortion rates up to 60%.

Tip

The job of a disease detective also involves educating the public about abortion storms on goat farms and working to educate the public, veterinarians, physicians, and the news media.

As the lead disease detective on this case, you also need to think about health education and ways to educate the public about Q fever. It's your job to create strategies for educating the public and trying to change health behaviors to prevent a new outbreak.

You recommend and help the government create a mass education program, complete with materials targeted to the public, veterinarians, physicians, and the news media.

Notes

The job of a disease detective also involves making recommendations about veterinary measures which can help control the outbreak.

To help stop the spread of Q fever, you recommend to the government various veterinary measures, including new hygiene procedures, limiting the movement of goats/sheep, and placing a temporary ban on new breeding. Based on your research, you believe that these measures will control the outbreak.

However, the federal government decides to make a controversial decision to slaughter more than 50,000 dairy goats on 55 of the country's nearly 400 farms to prevent the disease from spreading further.

Data

The above table shows which characteristics were more likely to cause people to take preventative measures.

Last, you research the effectiveness of the educational campaigns you recommended. You'd like to identify trends and regional differences in public opinions and behaviors. As a disease detective, you want to learn which measures were most effective in improving awareness of Q fever and increasing the number of people who took preventative measures to protect themselves. So, you decide to conduct a study to learn more.

In your study, you find that public knowledge about Q fever increased significantly during the outbreak. You also learn that the assumed severity of the disease also increased among the public.

However, the most surprising thing you learn is that even though more people were aware of the diseases and the severity, there were low levels of vulnerability (only 15% of people thought that they were susceptible to getting Q fever) presumed.

Clue 1

Craig sees the doctor since he hasn't been feeling well lately.

Four days after returning from an epic spring break trip, Craig and 2 of his housemates went to the campus clinic with fever, chills, and body aches. These are common flu symptoms and it is flu season, but there hasn't been much flu on campus this year.

Craig is the first to see the doctor, who runs a rapid test for influenza (flu). The test comes back positive. Knowing that the 3 fraternity brothers are housemates, the doctor thinks that they all probably have the flu. She suggests that they stay in their rooms to avoid getting others sick and get some rest

Cases

Jordan has been in bed with a fever of over 102°F.

When Craig arrived at the clinic he reported pain all over his body, fever, an intense headache, and coughing.

Brian and Jordan, who came to the clinic with Craig, had fevers above 102°F. Brian said it started when he was in class the previous afternoon. He walked into class feeling fine, but suddenly felt like something was wrong, and when class was over he was so tired he headed straight to bed. Jordan said he felt bad earlier in the day, with a headache that didn't let him concentrate.

The next morning, Jordan went back to the clinic feeling worse and with an odd-looking rash on his chest. The doctor was concerned and ordered a flu test.

As Jordan waited for the result, 3 more sick frat brothers came in. Each of them had a fever, two reported splitting headaches and one had nausea. He said he felt like his "bones were breaking"!

These symptoms are concerning and seem less like flu. When Jordan's flu test comes back negative, the doctor calls a Disease Detective for help!

Definition

This woman feels nauseous.

Nausea (noun): the feeling you have in your stomach when you think you are going to vomit.

Clue 2

Several brothers are experiencing severe bruising.

The phone at the clinic has been ringing off the hook all day with worried parents calling to find out what is wrong with their sons. Meanwhile, the blood tests come back with evidence of a viral infection that is not the flu.

In the last couple of hours, 3 of the 6 sick fraternity brothers have been admitted to the hospital. Their blood cell counts are low, which can result in severe bruising, nose bleeds, and bloody gums!

To make matters worse, the clinic just found out that there are 4 more sick fraternity brothers with symptoms similar to the other guys!

In the course of interviewing the patients, you find out that 20 fraternity brothers went on a trip to the Caribbean. They had been planning the trip ever since Craig had found a deal on some bungalows near the beach.

Data

Epidemic curve of the fraternity brothers' trip to the Caribbean relative to when they became ill.

You also learn that the fraternity brothers spent 7 days and 6 nights in the Caribbean. They returned to campus on March 22nd, the day before classes were back in session.

To get a better handle on the data you've collected, you make an epidemic curve, which can help you determine the pathogen (bacteria or virus) that's infected the brothers.

Since all of the brothers got sick 2-6 days after returning to campus, you look for a pathogen that has an incubation period (the time from when a person gets infected to the time when symptoms start) of 3 to 12 days.

Definition

Epidemic curve of the fraternity brothers' trip to the Caribbean relative to when they became ill.

An epidemic (epi) curve shows how an outbreak changes over time. It includes:

• Date when a person became sick.
• Number of people who became sick on each day.

• Point source — the sick people came into contact with the source of the outbreak for a short time. This is kind of outbreak usually has an epi curve with a single peak.
• Continuous common source — the sick people came into contact with the source of the outbreak over a longer period of time (i.e. months, years, etc.). The epi curve increases slowly over a long period of time and might level off.
• Propagated outbreak — there may be an initial common source but then sick people transmit the pathogen to others, creating a larger outbreak. The epi curve may look like a point source curve initially, but then has repeated peaks, which indicate new transmission cycles.

Learn more about epi curves.

Notes

The brothers hung out by the pool while on vacation.

The brothers had to unexpectedly share their bungalows with some annoying mosquitoes, and after 1 night of being bitten, half of the group left and got hotel rooms. But they didn't let this pesky setback ruin their vacation. In fact, they met up every day to hang out and soak up the "island life"–trying local cuisines (including foods that may not have been cooked in the most sanitary conditions), surfing, hiking, and lounging by the pool.

From what they remember, no one felt sick on the trip.

Clue 3

You review your notes to find what may have caused the sickness.

You take a closer look at the activities each fraternity brother participated in while on vacation. Maybe there is a link between a specific activity and the illness.

The doctor calls to let you know that another fraternity brother stopped by the clinic with similar symptoms as his friends. That brings the total case count to 11!

Data

Table of attack rates by activities that sick and well fraternity brothers participated in while on vacation in the Caribbean.

You organize the list of activities that each fraternity brother did on vacation into a table. Then, you calculate the attack rate for each activity based on those who did and did not participate. If any activity stands out, it may be a potential cause or link to the sickness.

Tip: To identify the likely source of the outbreak, look for an activity that has a high attack rate among those who performed a specific activity AND a low attack rate among those who did not.

Clue 4

Aedes aegypti mosquitoes like this one can transmit dengue and other infectious diseases.

After deciding that this outbreak may have been caused by a mosquito-transmitted pathogen, you ask the doctors at the clinic and hospital to order tests for mosquito-borne diseases. A few days later, lab tests for several patients come back positive for dengue virus infection. Dengue viruses are transmitted through the bite of infected mosquitoes. People with dengue can have fever, headache, body and eye pain, weakness, and in some cases bleeding (i.e. bruising and nosebleeds).

The fraternity brothers were probably exposed to the virus at the bungalows, since that's where they all stayed for at least 1 night. While all of the brothers reported at least a few bites, even those who didn't get sick, some may have been bitten by mosquitoes that weren't infected with the virus.

Notes

The tropics, including the Caribbean, are endemic for dengue.

The species of mosquito that transmit dengue are Aedes aegypti (ay-deez ə-gyp-tai) and Aedes albopictus (ay-deez al-boh-pik-tus), which live in and around homes and typically bite people during the day. Although they are usually most abundant in the summer months, these mosquitoes are present year round. So, people who live in or travel to tropic or sub-tropics regions, including the Caribbean, can get sick with dengue at any time of the year. (Areas where a disease is naturally occurring are referred to as endemic regions).

It usually takes 4-10 days to begin feeling sick after being bitten by an infected mosquito. Common symptoms of dengue include fever, aches and pains, rash, fatigue, and minor hemorrhagic manifestations (e.g., nose bleed, unusual bruising, bleeding from the gums, etc.).

Although there is no specific medication or vaccine available to treat or prevent dengue, seeking medical attention at the early stages of the illness can reduce the likelihood of death for people who may experience more serious symptoms. The best way to avoid getting dengue is to wear mosquito repellent, and sleep in places that have air conditioning and/or screens on windows and doors.

Clue 5

Alex has been hospitalized and may have dengue fever.

Now that you've figured out what made the fraternity brothers sick, your job is over, right? Not quite!

You receive a call from the university clinic informing you that another fraternity brother, Alex, has been hospitalized with what they suspect are dengue-like symptoms. However, Alex stayed on campus during spring break and it's been about 3 weeks since the brothers returned from the Caribbean! What's going on?

Health Tips

Using mosquito repellent can protect you against diseases like dengue.

One of the biggest risk factors for getting dengue is having a household member or neighbor who recently had the illness. This is because the mosquitoes that transmit dengue (Aedes aegypti and Aedes albopictus) live nearby and inside homes. When someone is home sick with dengue, the mosquitoes feed on them and then become infected. After 10 days or so, the mosquitoes become infectious and can transmit the virus to humans when they feed again.

If you reside in a part of the world that has Aedes mosquitoes and live in the same household or near someone who has dengue, it's very important to take the following steps to protect yourself:

• Wear mosquito repellent.
• Stay in housing with air conditioning and/or screens on windows and doors.
• Empty any water-containers that have standing water and can therefore serve as mosquito breeding sites.
• Seek medical care if you experience an illness with fever and tell the doctor that you live close to someone who recently had dengue.

Data

Epidemic curve of when each sick fraternity brother became ill.

It looks like the fraternity brothers introduced the dengue virus to campus. Since there are mosquitoes in the area that can carry the disease, a few probably bit the sick brothers and are now infecting others. In other words, there's a local dengue outbreak!

To confirm your suspicion that the 2 outbreaks are linked, you update the epi curve to see if the time sequence matches.

Clue 1

A sick elementary student at the school clinic.

It's early June, the last week of school for this California community, and everyone's getting ready for summer break. But the worst illness of the year has waited until now to rear its head!

Over a 3 day period, 1 county health department received reports of 25 kids and 3 adults who are sick with diarrhea, vomiting, fever, and stomach cramps. All but 2 of the sick kids go to the same elementary school. One of the sick adults is a teacher at the school, too.

The health department follows up with the doctors who've been treating the cases and learns that several physicians have ordered lab tests on their patients' stool samples to see what kind of infection is causing their symptoms. The tests indicate Salmonella, a type of bacteria.

The health department then asks the hospital laboratories to send the isolates to the public health laboratory so they can determine the "DNA fingerprint" of the Salmonella bacteria. Just like humans, Salmonella bacteria have unique "DNA fingerprints".

As you compare the test results, you realize that the "DNA fingerprints" match for all of the sick people, which means that they're infected with the same strain of Salmonella. From now on, we'll call this the "outbreak strain".

You need to find out what the source of the outbreak is before more people get sick!

Data

The epi curve shows you when people first became sick.

One of the first things you need to do is to make an epidemic curve, which is also known as an epi curve. This shows how an outbreak changes over time. It includes:

• Illness onset, which is the date when a person first became sick.
• Number of people who became sick on each day.

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak.

Learn how to read an epi curve.

Definition

A magnified picture of Salmonella bacteria.

What is Salmonella?

Salmonella is a bacterium that causes an infection called salmonellosis. Most people infected with Salmonella get diarrhea, fever, and abdominal cramps 12 to 72 hours after they're infected. The illness usually lasts 4 to 7 days, and most people recover without treatment.

For some people, like children under the age of 5, people with weakened immune systems, and older adults over the age of 65, the illnesses can be more severe. Sometimes the diarrhea can be so bad that the person needs to be hospitalized. In some cases, the infection can spread from a person's intestines to the blood stream, and can cause death unless treated promptly with antibiotics.

Although the majority of infections are foodborne (e.g., from animal or plant-derived foods), zoonotic (from infected animals) Salmonella infections are an important public health problem.

Notes

This is a computerized image of a DNA molecule.

DNA is short for deoxyribonucleic acid, which carries genetic information in the cells of animals, plants, bacteria, and some viruses. DNA provides instructions on how living organisms and viruses should look, grow, and sometimes behave. It can also be used to identify one organism from another, just like a fingerprint.

Clue 2

Many of the kids went on a field trip days before feeling sick.

Most of the sick kids go to the town's main elementary school. One of their teachers, Lisa, isn't sick, but she blames herself for the illnesses. She took a large group on a field trip to the local community garden on May 16, and she wonders if the kids ate something bad at the picnic. They had brought boxed lunches from the cafeteria, but she wonders if she left them out in the heat too long before the kids ate them.

She's also worried that some of the kids played in the small stream at the garden, as there were posted signs warning that it might have high levels of bacteria in it.

Data

You gather information about what people did the week before they got sick.

You interview the sick people and the parents of the sick children to find out what the cases have in common. You need to find out what foods they ate, what activities they did, and what kinds of animals they've been around during the week before they got sick.

Since most of them went on the school field trip, a lot of the cases ate the same foods. You notice that many of them also have pets at home, which can spread germs to people.

In addition to the sick kids who went on the field trip, there are two sick kids and one sick adult who don't seem to have any connection to the school.

Health Tips

Use a food thermometer while cooking to check the temperature of meat and poultry before you eat it.

To avoid Salmonella infection, be sure to:

• Cook meats, casseroles, and other dishes containing eggs to the proper internal temperature using a food thermometer. Cook eggs until both the yolk and the white are firm. Scrambled eggs should not be runny.
• Avoid foods containing raw (unpasteurized) milk or raw eggs.
• Wash hands, kitchen work surfaces, and utensils with soap and water immediately after they have been in contact with raw meat or poultry.
• Be particularly careful with foods prepared for children under 5 years, older adults over the age of 65, and people with weakened immune systems, including pregnant women.
• If you are served undercooked meat, poultry, or eggs in a restaurant, don't eat it and send it back to the kitchen for further cooking.
• Wash your hands after touching animals or anything in the area where they live and roam.

Clue 3

Most of the kids on the field trip planted seeds and dug in the dirt.

Most of the sick people (26 out of 28) went to the community garden. Twenty of them came as part of the school field trip on a Friday, and another 6 went there the next day. You ask one of the teachers, Lisa, more about the field trip to find out what her kids did.

She tells you that 75 kids from her school visited the garden. A gardener showed them where they grow vegetables and flowers, and the kids helped dig holes and plant seeds in the soil. After lunch, they played in a sand box and in an adobe hut. A few visited the chicken coop and a couple others played in the nearby stream. She doesn't think any of them visited the beekeeper's area or the goat pen.

Bad news: 5 more people from the same community have been identified with the outbreak strain of Salmonella! But this doesn't necessarily mean that they were infected by the same source as the earlier group of sick people. You'll need to work quickly to find out if there is a connection between the two groups.

Data

What could have gotten the people sick?

To get a better sense of what it was at the community garden that potentially made people sick, you also need to talk to people who went to the community garden but aren't sick. So you talk to every child (or their parent) and teacher who went on the field trip, whether they later got sick or not.

You need to ask each person what they did at the garden so you can calculate the "attack rate" for each exposure that might have made people sick. So, you quickly to try to contact as many of the sick and well persons who went on the field trip. You were able to interview 20 sick people and 55 people who didn't get sick about what they did at the garden.

Tip

What could have gotten the people sick?

To identify the likely source of the outbreak, look for a high attack rate among those who participated in a specific activity AND a low attack rate among those who did not participate.

Clue 4

It looks like the kids had more contact with chickens than they realized.

It might seem strange that two seemingly unrelated things would both have pretty high attack rates. But then you talk to one of the workers at the community garden, and it starts to make more sense!

It turns out that the night before the field trip someone forgot to latch the door of the chicken coop. When the gardener showed up early Friday morning, the chickens were loose! They were having a great time digging around in the sandbox and searching for scraps of food under the picnic tables. Since the chickens spent most of the night in and around the sand box, they left chicken droppings behind. They were eventually rounded up and put away in their coop just before the school kids arrived.

Notes

They're cute and fluffy but some animals, like baby chicks, can carry Salmonella.

It's important to remember that you don't have to eat contaminated food to get sick with a Salmonella infection. You can also get it from live animals that carry the bacteria in their intestines or on their bodies whether they have skin, scales, feathers, or fur. Also, anywhere the infected animals live and roam can be potentially contaminated with harmful bacteria that can make people sick even if they didn't touch the animals.

Laboratory tests confirm that the community garden's chickens have the same strain of Salmonella as the sick people. So it's safe to say that the infected chickens spread their germs around the garden when they escaped from their coop. Since the chickens spent a lot of time in the sandbox, the kids who played in the sand and later put their hands in their mouths or noses (yuck!) were most likely to get sick.

Other people may have gotten infected if they touched the chickens or anything in the coop area without washing their hands afterward.

Cases

This magnified image of the Salmonella strain has a DNA fingerprint that looks like the strain that's infected people in 2 far-off states.

Your colleagues at the Centers for Disease Control and Prevention have been carefully monitoring PulseNet, a national database of bacterial DNA fingerprints to see if anyone else has been infected with the outbreak strain of Salmonella. Sure enough, there are 18 other people who have been infected with Salmonella with the same DNA fingerprint but they live in Missouri and Wyoming, hundreds of miles from California!

Your colleagues in Missouri and Wyoming work to contact the 18 sick people to find out what they might have in common with the ill people in California.

Clue 5

Your colleague interviews local cases to get information that may help solve the outbreak.

You need to figure out how the sick people in Missouri and Wyoming became ill with the outbreak strain of Salmonella.

Your colleagues in Missouri and Wyoming are able to interview the additional 18 sick people, and you learn that 16 of the 18 people recently had contact with chickens. In fact, 11 of the 16 said they have chickens in their backyards, and they tell you they recently bought these chickens from several different feed stores. (Feed stores are places where people can buy some types of animals, animal feed, and farm supplies.)

The next thing you try to find out is where the people in California, Missouri, and Wyoming got their chickens.

Cases

Farm animals, such as baby chicks and other poultry, are often sold and shipped around the country, making it easier for bacteria, such as Salmonella, to spread to multiple states.

You learn that all of the feed stores identified in the traceback investigation got their chickens as baby chicks from the same mail-order hatchery in Kansas, as did the community garden in California. A mail-order hatchery is a company that hatches and sells baby chicks, ducklings, and other baby poultry to consumers and feed stores.

It turns out that the mail-order hatchery supplies chicks to customers in Wyoming, California, and Missouri. The outbreak strain of Salmonella likely started at the mail-order hatchery and infected the chicks, which were then shipped to feed stores. People who bought the chicks from feed stores brought them home and got infected.

To confirm your theory, you travel to Kansas to conduct tests for Salmonella bacteria at the hatchery. Not only do you find Salmonella at the hatchery, it matches the DNA fingerprint of the outbreak strain that infected the sick people in California, Wyoming, and Missouri.

Definition

Traceback investigations are used to determine the source of contamination during an outbreak.

A traceback investigation is conducted to find the ultimate source of contamination during an outbreak. Information is gathered such as purchase receipts, invoices, and shipping records to determine where the outbreak first started. These investigations usually involve many partners in human and animal health agencies at the local, state, and federal level.

The information gathered during traceback investigations can also help suggest ways to prevent similar outbreaks from happening in the future.

Health Tips

It's important to always wash your hands after touching an animal.

To help avoid Salmonella infection from live poultry, follow these simple tips:

DO

• Wash hands thoroughly with soap and water right after touching live poultry or anything in the area where they live and roam. Use hand sanitizer if soap and water are not readily available. (Adults should supervise hand washing for young children).
• Clean any equipment or materials associated with raising or caring for live poultry outside the house, such as cages or feed or water containers.

DON'T

• Don't let children younger than 5 years of age, older adults, or people with weakened immune systems handle or touch chicks, ducklings, or other live poultry.
• Don't snuggle or kiss the birds, touch your mouth, or eat or drink around live poultry.
• Don't let live poultry inside the house, in bathrooms, or especially in areas where food or drink is prepared, served, or stored, such as kitchens or outdoor patios.
• Don't give live baby poultry as gifts to young children.

Clue 1

An inmate at Bensil prison.

Sam is an inmate and kitchen staff member at Bensil federal prison. One night, while loading dishes, he notices a rash with a few itchy blisters on his arm. He goes back to his cell and finds more blisters on his chest and stomach so he decides to visit the prison's health clinic. The doctor thinks Sam has bug bites, since there's been a recent problem with bed bugs in the prison. He sends Sam back to his cell with cream for his skin rash. The next day Sam is feeling a little better and goes back to work in the kitchen.

Over the next two weeks, 9 other inmates complain of not feeling well and very itchy rashes that have kept them up all night. Some have also had fever and felt very tired. Greg, a prison guard, has also developed a rash with fever. All of the sick inmates rush to the health clinic demanding creams, pills, basically anything that will relieve the itchiness and fever.

Since there are many cases of rash illness occurring in a short period of time, the doctor suspects that he may have an outbreak on his hands. There are many things that can cause rashes, but the doctor suspects chickenpox.

Cases

Medical logs and records will help you find who has been sick.

You start your investigation by checking the medical logs and records of any inmate who was treated for a rash in the prison health clinic in the last 4 weeks. Since you think this might be chickenpox, you look up the chickenpox clinical case definition: An illness that includes a rash with red bumps and/or fluid-filled blisters that are all over the body (generalized) without another known diagnosis.

Based on the clinical definition, you organize the medical records of the inmates that have rashes into two piles, probable cases and confirmed cases of chickenpox. You also start to collect specimens, like blister fluid and scabs from as many cases as possible for lab tests to help you figure out what's causing the rashes.

Definition

A nurse looking through patient files.

What is a clinical case definition?

A clinical case definition is used to figure out who should be included in an outbreak investigation. A different case definition is used depending on the type of suspected illness.

The clinical case definition for chickenpox is: An illness that includes a rash with red bumps and/or fluid-filled blisters that are all over the body (generalized) without another known diagnosis.

In this situation, the clinical case definition for chickenpox is used to figure out who has the disease, which is known as a confirmed case and who might have the disease, which is referred to as a probable case.

• Confirmed case of chickenpox: A person who has a positive lab test or has symptoms of chickenpox (meaning that they meet the clinical case definition) and is linked to another confirmed or probable case.
• Probable case of chickenpox: A person who has symptoms of chickenpox (meaning that they meet the clinical case definition) but does not have a positive lab test or is not linked to another probable or confirmed case.

Notes

This person's back shows what a chickenpox rash looks like.

Chickenpox is caused by a virus that spreads easily from an infected person to others who have never had the illness or received the chickenpox vaccine. It can be spread by:

• Breathing in virus particles that come from chickenpox blisters or by the cough or sneeze of an infected person.
• Touching the virus particles that come from chickenpox blisters.

It takes 10 to 21 days after exposure for someone to develop chickenpox.

Symptoms usually include:

• Blister-like rash
• Itching
• Tiredness
• Fever

A person is infectious, meaning they can spread the disease, starting 1 to 2 days before they get the rash, up until all of their chickenpox blisters have formed scabs. Chickenpox can be serious, especially in babies, adults, and people with weakened immune systems. Some people develop complications, like pneumonia, which can lead to hospitalizations, and even death.

Clue 2

Doesn't look like the prison lockdown will end anytime soon.

You receive word that Sam's kitchen supervisor has been hospitalized with pneumonia and has a severe rash, with hundreds of blisters covering his body.

In order to learn more about the disease that's devastating the prison, and identify who may have been exposed and who needs to be placed in quarantine, you interview and gather information from the confirmed and probable cases. Then, you create a line list to figure out where the outbreak may have started and where you should focus your investigation.

As you work, 5 more inmates visit the clinic with a rash on their hands and arms. With these new cases popping-up, it doesn't look like the prison lockdown will end anytime soon. The prisoners are getting restless and medical supplies, like anti-itching creams, are running low!

Better work fast!

Data

You create a line list of rash cases.

A line list is a table that has key information about each sick person. Each row represents a case (sick person), and each column has important information about the case, like age, sex, and symptoms. Other characteristics like where a person lives or works can also be included in a line list to help determine what characteristics put a person at higher risk of becoming a case.

Clue 3

Lab workers finish examining samples that will confirm the source of the rash.

Lab results are back and confirm that the hospitalized prisoner along with the sick inmates from Unit A and the guard have chickenpox. However, the 5 inmates from the other housing units do not. Their lab results are negative for chickenpox.

You remember from the line list that all 5 inmates work in the laundry room. After a short interview with one of them you learn that the prison recently changed laundry detergents. Since each inmate only has a rash on their hands they have been diagnosed with contact dermatitis.

Now you can focus your efforts on the inmates in Unit A, since that's where all of the confirmed cases live. You consider all Unit A inmates exposed, which is about 100 people. But you discover that only 21 inmates had close contact with cases, so you quarantine them immediately.

Notes

Contact dermatitis can be caused by your skin touching irritants or allergens, like some foods or chemicals.

What is contact dermatitis?

Contact dermatitis is a condition where the skin becomes red, sore, or irritated after touching something that you're allergic to or an irritant (such as a chemical). It's not life threatening, but can be very uncomfortable. It can lead to itchy or burning rashes.

Contact dermatitis isn't contagious, which means it can't spread from one person to another. The rash only appears soon, sometimes even minutes, after touching something that you're allergic to. The rash usually occurs only on the part of the body that touched the substance.

Contact dermatitis can be mistaken for chickenpox since both lead to an itchy rash with red bumps. Both can also initially start in only one location. However, the chickenpox rash will usually spread to the rest of the body.

Cases

Inmates have been stuck in isolation and quarantine.

The guards are overworked and tired from working double shifts to monitor the inmates in isolation and quarantine. Even worse, inmates are becoming restless and unruly because they can't have any visitors or even have their meals in the cafeteria. You need to quickly figure out who of these 21 inmates is at risk for getting chickenpox and who has evidence of immunity (protection against chickenpox). This will help you decide who should be removed from quarantine.

Definition

CDC recommends two doses of chickenpox vaccine for children, adolescents, and adults.

Evidence of immunity to chickenpox means a person has proof of protection against the disease. If you meet at least 1 of the following criteria, then you have evidence of immunity to chickenpox:

• You were born in the United States before 1980.
• You received 2-doses of chickenpox vaccine.
• You have laboratory evidence of having the disease in the past or you have confirmation of current disease from a laboratory.
• You have confirmation from a healthcare provider that you have had chickenpox or shingles in the past.

You DO NOT have evidence of immunity to chickenpox if you do not have any of the above.

Birth in the United States before 1980 should not be considered evidence of immunity for health care personnel, pregnant women, and immunocompromised persons.

Data

Who among the exposed inmates are protected against chickenpox?

You create another table to figure out who among the 21 exposed inmates have evidence of immunity.

Clue 4

Just when you thought you had stopped the outbreak you get a call about an outbreak at Gaplin prison.

Just as you're getting a handle on the situation at Bensil, you receive a call from Gaplin Prison, which is another correctional facility in the area. Eight inmates at Gaplin have chickenpox! You immediately wonder if the two outbreaks are linked. After all, prisons share staff and inmates are sometimes transferred between prisons. You head to Gaplin to learn more about the inmates with chickenpox and what could have started the outbreak.

Cases

Greg, the guard from Bensil prison, also works at Gaplin prison.

You learn that Carl, one of the inmates with chickenpox from Bensil, was on the same bus with inmates from Gaplin 7 days before his rash developed. The bus was pretty full, so he sat right next to a few of the Gaplin prisoners during the ride.

Moreover, Greg, the sick guard from Bensil prison also works at the Gaplin facility. Greg is newly married and has a baby on the way so he picks up extra shifts whenever he can. He was on duty at Gaplin the day before he developed a rash.

Data

An epi curve of chickenpox cases from both prisons.

To find out who caused the outbreak you need to know when it started. After speaking with the sick Gaplin prisoners you find out that the first inmate became sick on March 11. To see if the two outbreaks are related you make an epi curve showing the chickenpox outbreak at each prison.

Definition

An epi curve of chickenpox cases from both prisons.

What's an epidemic curve (epi curve)?

An epi curve shows how an outbreak changes over time. It includes:

• Date when each person became sick.
• Number of people who become sick on each day.

Epi curves are updated as new data come in, so they are always changing. The shape of the curve can provide clues about the possible source of an outbreak, or how the outbreak may have started. It also helps to show you whether the outbreak is reaching a peak or if it's coming to an end.

Learn how to read an epi curve.

Clue 5

Time to get these prisons back to business as usual.

It's been 28 grueling days of quarantine for the exposed prisoners and relentless double shifts for the guards! The prison wardens at both facilities are anxious to return to their normal routines and activities. The inmates are eager to be let out of their cells and have visitors again.

While in quarantine, 3 of the 8 exposed Bensil prisoners ended up getting sick with chickenpox. The others did not.

Now that you know what the disease is and how it spread, you work to make sure the outbreak is completely over.

Clue 1

Laura practicing for her big game.

Laura is a 16-year-old high school junior who hopes to go to college on a softball scholarship in a couple of years. She's been practicing for her upcoming softball game, when suddenly she and two of her teammates come down with a fever, cough, and extreme tiredness. Worried, the softball coach sends the girls home. Five other students also come down with similar symptoms on the same day.

Desperate to get better and not miss another game, Laura and her friends head to the urgent care clinic to get checked out. While doctors are waiting for test results, more calls start coming in about similar illnesses.

Data

Patient information you gathered.

You gather medical records of the 15 sick people and ask them questions to see what they have in common.

Most of them have the following symptoms:

• Cough
• Sore throat
• Weakness
• Fever (as high as 105 degrees)

One person also has nausea, and 2 others feel light-headed and dizzy.

Clue 2

Students across the county feel sick.

The illness is spreading quickly. There are now 24 sick people! Laura and most of her friends are so sick that they've been out of school for more than a week. Worse, a 2-year-old boy and a 3-year-old girl have been hospitalized. The tests come back positive for an influenza (flu) virus infection, that's caused by a very unusual influenza virus.

It turns out that most of the sick people are students, but they go to different schools in a large county. You need to figure out how the illness could have spread across schools so fast.

Definition

Flu viruses are constantly changing; here is a 3D image of a generic influenza viral structure.

What is novel influenza?

Seasonal flu is a respiratory disease (a disease affecting the lungs) caused by seasonal influenza viruses. These are viruses that spread in people and cause flu epidemics every year, usually in the fall and winter months in the United States. Flu is usually spread from close contact with people via coughing or sneezing. Seasonal flu viruses are constantly changing, which means that the flu viruses that infect people one year can be different from the flu people get sick with the next year. This is one reason why you need to get a flu vaccine every season. Each season's vaccine is tailored to match what experts predict will be the most common viruses that season.

Novel flu viruses are viruses that are not usually seen in people—these viruses normally only infect animals such as birds or pigs. But they can infect people too, and even change in ways that let them spread between people like seasonal flu. Although novel flu virus infections are rare, they can be dangerous because seasonal flu vaccines usually don't protect against them and people usually won't have much natural immune protection against them.

Data

You need to figure out which activity may have led to the illness.

You decide to interview the sick teenagers, with the consent of their parents.

Based on the information you gathered, you see that they have a few things in common. Many of them played in or attended a state-wide baseball and softball tournament in Freemont, featuring teams from all across the state. Also, the county fair was recently in town, attracting big crowds. A few of the sick teenagers have traveled to other states and even other countries.

In order to get a better idea of how the sick teens were first exposed to this particular novel flu virus, you need to take a closer look and see how they spent their time over the past few weeks. You also need to interview a number of healthy teens who did those same activities. (We call this a case-control study.)

Tip

What could have gotten these girls sick with the flu?

To figure out which activity most likely led to flu exposure, search through the data table to find the activity with the highest value for prevalence (which means the proportion of a population that has a certain condition) among sick teens AND the lowest value for prevalence among healthy teens.

Clue 3

You need to figure out what it was about the fair that caused some people to get sick.

The illness is spreading! There are now 54 sick people, including 9 adults. According to a recent update, a 67-year-old man and 3 kids are in the hospital.

You meet with the fair organizers who say that more than 10,000 people came to the fair during the 5 day event. There were carnival rides, food stands, a concert, a barn dance, and a number of animal exhibits. Of course, many people who went to the fair are perfectly healthy.

Since this is a novel flu virus with no other cases reported, you suspect that it may have come from an animal. You take a closer look at what kinds of animals the sick people were exposed to.

Data

You need to figure out what animal may have spread the disease.

As you talk to the sick and healthy teens who went to the fair, you're especially interested in the types of animals they were around. Some animals get the flu too, but their flu viruses usually aren't passed on to people. However, every now and then, an animal's flu strain (or type of flu) changes in a way that allows it to be spread among people easily.

You learn that many of the sick and healthy teens that you interviewed spent time around cows, chickens, and pigs. Some of them only spent an hour or two with animals, and some spent as many as 10 hours with them.

Clue 4

The new flu virus has quickly spread across the country.

It's been 19 days since Laura and her friends first got sick from this novel flu. There are now at least 72 sick people in this county alone, 11 have been hospitalized, and one person has died!

It also looks like the flu crossed the state line! You talk to health departments across the country and learn that there are at least 4,000 confirmed cases in 36 states, with dozens of people hospitalized. From the looks of it, you have a large outbreak on your hands, which may even turn into a pandemic!

With the number of cases quickly rising you begin to wonder whether all of these people attended the county fair or if they got infected somewhere else.

Definition

CDC experts are constantly on watch for new flu viruses. When a new virus can be transmitted from person to person, it might cause a pandemic.

What's a pandemic?

A pandemic occurs when a disease spreads and affects a very large number of people across the globe.

Scientists monitor novel flu viruses carefully. A novel flu virus might cause a pandemic if the virus can spread efficiently from person to person and if most people don't have any immunity to the new virus. If the new flu virus can only be spread from animals to people or from one person to another, but no further, then it probably won't cause a pandemic. People can have some immunity to flu viruses that are similar to viruses they've had in the past. If a new flu virus is very different from earlier flu viruses, it may be more likely to cause a pandemic.

Though most people recover from seasonal flu after a week or two, a small percentage of people with flu die every year. A novel flu virus could be much more serious, and if a novel flu virus caused a severe pandemic, many people could die. This happened during the 1918 influenza pandemic, during which millions of people died.

Data

Why is the flu spreading so quickly?

After careful consideration, you rule out the possibility that all of the new cases that are popping up across the country are a result of people attending the county fair. You arrange a virtual meeting with health departments across the United States to get more information about the cases.

Based on the information you gathered, you calculate the relative risk to figure out why so many people are getting sick.

Tip

Why is the flu spreading so quickly?

Relative Risk (RR) describes the likelihood of some event (like getting food poisoning) occurring in a group of people with a potential risk factor (like eating spinach) compared to a group without that risk factor (in this example, not eating spinach). If the RR of getting sick after eating contaminated spinach was 5, then people who ate contaminated spinach would be 5 times more likely to get sick than people who did not eat contaminated spinach. The closer the relative risk is to 1, the greater the likelihood that an event occurring (like getting food poisoning) is about the same for both groups.

Clue 5

The new flu virus is now a worldwide problem.

After confirming your suspicion that the new flu virus is now being spread from person to person, you work with other experts at the Centers for Disease and Control and Prevention (CDC), as well as state health departments across the country, to keep track of the number of people who are sick. At last count, there were at least 52,100 sick people, 1,702 people in the hospital, and 94 deaths.

Worse, you learn that there are now thousands of cases in different countries. People are scared; the story of the new flu is all over the newspapers, Internet, and TV news! You tell people to stay home from work or school if they feel sick, so they don't spread the flu to others.

Health Tips

Basic steps like washing hands and not touching your face can go a long way.

To reduce your chances of getting the flu, follow these steps:

• Get a flu vaccine every year. This is the most important step in protecting yourself against seasonal flu viruses. Everyone 6 months of age and older, with a few exceptions, should get a seasonal flu vaccine.
If a vaccine is made to protect against a novel influenza virus, get that vaccine too. Try to avoid close contact with sick people. If you are sick with flu-like illness, stay home for at least 24 hours after your fever is gone except to get medical care or for other necessities. (Your fever should be gone without the use of a fever-reducing medicine.) While sick, limit contact with others as much as possible to keep from infecting them. Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it. Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub. Avoid touching your eyes, nose, and mouth. Germs spread this way. Clean and disinfect surfaces and objects that may be contaminated with germs like the flu.