Overview
A foodborne disease outbreak is defined as an incident in which two or more persons experience a similar illness resulting from the ingestion of a common food.* Foodborne disease outbreaks should be reported to CDC's Enteric Diseases Epidemiology Branch through the National Outbreak Reporting System (NORS).**
The following tables provide information about etiologic agents (causes), incubation periods, clinical syndromes, and criteria for confirmation of a case after a foodborne disease outbreak has been identified. The information on incubation periods and clinical syndromes is not part of confirmation criteria. These guidelines might not include all etiologic agents and diagnostic tests.
Guidelines for confirming cause of foodborne disease outbreaks
Bacterial Causes
| Etiologic Agent | Incubation Period | Clinical Syndrome | Confirmation |
|---|---|---|---|
| Bacillus cereus - Vomiting toxin | 1-6 hrs | Vomiting; some patients with diarrhea; fever uncommon | Isolation of organism from stool of two or more ill persons and not from stool of control patients
OR Isolation of 105 organisms/g from epidemiologically implicated food, provided specimen is properly handled |
| Bacillus cereus - Diarrheal toxin | 6-24 hrs | Diarrhea, abdominal cramps, and vomiting in some patients; fever uncommon | Isolation of organism from stool of two or more ill persons and not from stool of control patients
OR Isolation of 105 organisms/g from epidemiologically implicated food, provided specimen is properly handled |
| Brucella | Several days to several mos; usually >30 days | Weakness, fever, headache, sweats, chills, arthralgia, weight loss, splenomegaly | Two or more ill persons and isolation of organism in culture of blood or bone marrow; greater than fourfold increase in standard agglutination titer (SAT) over several wks, or single SAT 1:160 in person who has compatible clinical symptoms and history of exposure |
| Campylobacter jejuni/coli | 2-10 days; usually 2-5 days | Diarrhea (often bloody), abdominal pain, fever | Isolation of organism from clinical specimens from two or more ill persons
OR Isolation of organism from epidemiologically implicated food |
| Clostridium botulinum | 2 hrs-8 days; usually 12-48 hrs | Illness of variable severity; common symptoms are diplopia, blurred vision, and bulbar weakness; paralysis, which is usually descending and bilateral, might progress rapidly | Detection of botulinum toxin in serum, stool, gastric contents, or implicated food
OR Isolation of organism from stool or intestine |
| Clostridium perfringens | 6-24 hrs | Diarrhea, abdominal cramps; vomiting and fever uncommon | Isolation of 106 organisms/g from stool of two or more ill persons, provided specimen is properly handled.
OR Demonstration of enterotoxin in the stool of two or more ill persons OR Isolation of 105 organisms/g from epidemiologically implicated food, provided specimen is properly handled |
| Escherichia coli - Enterohemorrhagic (E. coli O157:H7 and others) | 1-10 days; usually 3-4 days | Diarrhea (often bloody), abdominal cramps (often severe), little or no fever | Isolation of E. coli O157:H7 or other Shiga-like toxin-producing E. coli from clinical specimen from two or more ill persons
OR Isolation of E. coli O157:H7 or other Shiga-like toxin-producing E. coli from epidemiologically implicated food |
| Escherichia coli - Enterotoxigenic (ETEC) | 6-48 hrs | Diarrhea, abdominal cramps, nausea; vomiting and fever less common | Isolation of organism of same serotype, demonstrated to produce heat-stable (ST) and/or heat-labile (LT) enterotoxin, from stool of two or more ill persons |
| Escherichia coli - Enteropathogenic (EPEC) | Variable | Diarrhea, fever, abdominal cramps | Isolation of organism of same enteropathogenic serotype from stool of two or more ill persons |
| Escherichia coli - Enteroinvasive (EIEC) | Variable | Diarrhea (might be bloody), fever, abdominal cramps | Isolation of same enteroinvasive serotype from stool of two or more ill persons |
| Listeria monocytogenes - Invasive disease | 2-6 wks | Meningitis, neonatal sepsis, fever | Isolation of organism from normally sterile site |
| Listeria monocytogenes - Diarrheal disease | Unknown | Diarrhea, abdominal cramps, fever | Isolation of organism of same serotype from stool of two or more ill persons exposed to food that is epidemiologically implicated or from which organism of same serotype has been isolated |
| Nontyphoidal Salmonella | 6 hrs-10 days; usually 6-48 hrs | Diarrhea, often with fever and abdominal cramps | Isolation of organism of same serotype from clinical specimens from two or more ill persons
OR Isolation of organism from epidemiologically implicated food |
| Salmonella Typhi | 3-60 days; usually 7-14 days | Fever, anorexia, malaise, headache, and myalgia; sometimes diarrhea or constipation | Isolation of organism from clinical specimens from two or more ill persons
OR Isolation of organism from epidemiologically implicated food |
| Shigella spp. | 12 hrs-6 days; usually 2-4 days | Diarrhea (sometimes bloody), often accompanied by fever and abdominal cramps | Isolation of organism of same species or serotype from clinical specimens from two or more ill persons
OR Isolation of organism from epidemiologically implicated food |
| Staphylococcus aureus | 30 min-8 hrs; usually 2-4 hrs | Vomiting, diarrhea | Isolation of organism of same phage type from stool or vomitus of two or more ill persons
OR Detection of enterotoxin in epidemiologically implicated food OR Isolation of 105 organisms/g from epidemiologically implicated food, provided specimen is properly handled |
| Streptococcus, group A | 1-4 days | Fever, pharyngitis, scarlet fever, upper respiratory infection | Isolation of organism of same M- or T-type from throats of two or more ill persons
OR Isolation of organism of same M- or T-type from epidemiologically implicated food |
| Vibrio cholerae - O1 or O139 | 1-5 days | Watery diarrhea, often accompanied by vomiting | Isolation of toxigenic organism from stool or vomitus of two or more ill persons
OR Significant rise in vibriocidal, bacterial-agglutinating, or antitoxin antibodies in acute- and early convalescent-phase sera among persons not recently immunized OR Isolation of toxigenic organism from epidemiologically implicated food |
| Vibrio cholerae - non-O1 and non-O139 | 1-5 days | Watery diarrhea | Isolation of organism of same serotype from stool of two or more ill persons |
| Vibrio parahaemolyticus | 4-30 hrs | Diarrhea | Isolation of Kanagawa-positive organism from stool of two or more ill persons
OR Isolation of 105 Kanagawa-positive organisms/g from epidemiologically implicated food, provided specimen is properly handled |
| Yersinia enterocolitica | 1-10 days; usually 4-6 days | Diarrhea, abdominal pain (often severe) | Isolation of organism from clinical specimen from two or more ill persons
OR Isolation of pathogenic strain of organism from epidemiologically implicated food |
Chemical Causes
| Etiologic Agent | Incubation Period | Clinical Syndrome | Confirmation |
|---|---|---|---|
| Marine toxins - Ciguatoxin | 1-48 hrs; usually 2-8 hrs | Usually gastrointestinal symptoms followed by neurologic symptoms(including paresthesia of lips, tongue, throat, or extremities) and reversal of hot and cold sensation | Demonstration of ciguatoxin in epidemiologically implicated fish
OR Clinical syndrome among persons who have eaten a type of fish previously associated with ciguatera fish poisoning (e.g., snapper, grouper, or barracuda) |
| Marine toxins - Scombroid toxin (histamine) | 1 min-3 hrs; usually 1 hr | Flushing, dizziness, burning of mouth and throat, headache, gastrointestinal symptoms, urticaria, and generalized pruritis | Demonstration of histamine in epidemiologically implicated fish
OR Clinical syndrome among persons who have eaten a type of fish previously associated with histamine fish poisoning (e.g., mahi-mahi or fish of order Scomboidei) |
| Marine toxins - Paralytic or neurotoxic shellfish poison | 30 min-3 hrs | Paresthesia of lips, mouth or face, and extremities; intestinal symptoms or weakness, including respiratory difficulty | Detection of toxin in epidemiologically implicated food
OR Detection of large numbers of shellfish-poisoning-associated species of dinoflagellates in water from which epidemiologically implicated mollusks are gathered |
| Marine toxins - Puffer fish, tetrodotoxin | 10 min-3 hrs; usually 10-45 min | Paresthesia of lips, tongue, face, or extremities, often following numbness; loss of proprioception or floating sensations | Demonstration of tetrodotoxin in epidemiologically implicated fish
OR Clinical syndrome among persons who have eaten puffer fish |
| Heavy metals (Antimony, Cadmium, Copper, Iron, Tin, Zinc) | 5 min-8 hrs; usually <1 hr | Vomiting, often metallic taste | Demonstration of high concentration of metal in epidemiologically implicated food |
| Monosodium glutamate (MSG) | 3 min-2 hrs; usually <1 hr | Burning sensation in chest, neck, abdomen, or extremities; sensation of lightness and pressure over face or heavy feeling in chest | Clinical syndrome among persons who have eaten food containing MSG (e.g., usually 1.5 g MSG) |
| Mushroom toxins - Shorter-acting toxins (Muscimol, Muscarine, Psilocybin, Coprinus artrementaris, Ibotenic acid) | 2 hrs | Usually vomiting and diarrhea, other symptoms differ with toxin
|
Clinical syndrome among persons who have eaten mushroom identified as toxic type
OR Demonstration of toxin in epidemiologically implicated mushroom or food containing mushroom |
| Mushroom toxins - Longer-acting toxins (e.g., Amanita spp.) | 6-24 hrs | Diarrhea and abdominal cramps for 24 hrs followed by hepatic and renal failure | Clinical syndrome among persons who have eaten mushroom identified as toxic type
OR Demonstration of toxin in epidemiologically implicated mushroom or food containing mushrooms |
Parasitic Causes
| Etiologic Agent | Incubation Period | Clinical Syndrome | Confirmation |
|---|---|---|---|
| Cryptosporidium spp. | 2-28 days; median: 7 days | Diarrhea, nausea, vomiting; fever | Demonstration of oocysts in stool or in small-bowel biopsy of two or more ill persons
OR Demonstration of organism in epidemiologically implicated food |
| Cyclospora cayetanensis | 1-14 days; median: 7 days | Diarrhea, nausea, anorexia, weight loss, cramps, gas, fatigue, low-grade fever; may be relapsing or protracted | Demonstration of the parasite by microscopy or molecular methods in stool or in intestinal aspirate or biopsy specimens from two or more ill persons
OR Demonstration of the parasite in epidemiologically implicated food |
| Giardia intestinalis | 3-25 days; median: 7 days | Diarrhea, gas, cramps, nausea, fatigue | Demonstration of the parasite in stool or small-bowel biopsy specimen of two or more ill persons |
| Trichinella spp. | 1-2 days for intestinal phase; 2-4 wks for systemic phase | Fever, myalgia, periorbital edema, high eosinophil count | Two or more ill persons and positive serologic test or demonstration of larvae in muscle biopsy
OR Demonstration of larvae in epidemiologically implicated meat |
Viral Causes
| Etiologic Agent | Incubation Period | Clinical Syndrome | Confirmation |
|---|---|---|---|
| Hepatitis A | 15-50 days; median: 28 days | Jaundice, dark urine, fatigue, anorexia, nausea | Detection of immunoglobulin M antibody to hepatitis A virus (IgM anti-HAV) in serum from two or more persons who consumed epidemiologically implicated food |
| Norovirus (NoV) | 12-48 hrs (median 33 hours) | Diarrhea, vomiting, nausea, abdominal cramps, low-grade fever | Detection of viral RNA in at least two bulk stool or vomitus specimens by real-time or conventional reverse transcriptase-polymerase chain reaction (RT-PCR)
OR Visualization of viruses (NoV) with characteristic morphology by electron microscopy in at least two or more bulk stool or vomitus specimens OR Two or more stools positive by commercial enzyme immunoassay (EIA) |
| Astrovirus | 12-48 hrs | Diarrhea, vomiting, nausea, abdominal cramps, low-grade fever | Detection of viral RNA in at least two bulk stool or vomitus specimens by real-time or conventional reverse transcriptase-polymerase chain reaction (RT-PCR)
OR Visualization of viruses (NoV) with characteristic morphology by electron microscopy in at least two or more bulk stool or vomitus specimens OR Two or more stools positive by commercial enzyme immunoassay (EIA) |
* Before 1992, three exceptions existed to this definition; only one case of botulism, marine-toxin intoxication, or chemical intoxication was required to constitute a foodborne disease outbreak if the etiology was confirmed. The definition was changed in 1992 to require two or more cases to constitute an outbreak.
** For information regarding the general criteria and confirmation tests used by the national Foodborne Disease Outbreak Surveillance System, refer to Centers for Disease Control and Prevention (CDC). Surveillance for Foodborne Disease Outbreaks, United States, 2013, Annual Report Cdc-pdf[PDF – 20 pages]. Atlanta, Georgia: US Department of Health and Human Services, CDC, 2015. For information regarding the collection of laboratory specimens and for additional information on viral agents, refer to "Recommendations for Collection of Laboratory Specimens Associated with Outbreaks of Gastroenteritis," MMWR 1990:39[No. RR-14] and "Viral Agents of Gastroenteritis: Public Health Importance and Outbreak Management," MMWR 1990;39[No. RR-5]).