Key points
- Poliovirus is highly contagious and causes polio, also called poliomyelitis, a serious and debilitating disease.
- Infection is more common in infants and young children.
- If you suspect polio, you should work with your state and local health department to order diagnostic testing.
Introduction
Poliovirus is a member of the Enterovirus genus, family Picornaviridae. Enteroviruses are transient inhabitants of the gastrointestinal tract and are stable at acidic pH. Picornaviruses are small, ether-insensitive viruses with an RNA genome.
Poliovirus is highly contagious and causes polio, or poliomyelitis, a serious and debilitating disease.
Poliovirus serotypes and immunity
How it spreads
The virus enters through the mouth and multiplies in the oropharynx and gastrointestinal tract. The virus is usually present in nasopharyngeal secretions for 1 to 2 weeks. It can also be shed in stools for several weeks after infection, even in individuals with minor symptoms or no illness.
Polio in children is more common
In temperate climates, poliovirus infections are most common during summer and autumn. In tropical areas, the seasonal pattern is less pronounced.
Polio transmission in the United States
There has not been a case of wild polio acquired in the United States since 1979. The last imported case of wild polio was in 1993.
Clinical features
Most people infected with poliovirus will not have any visible symptoms. About 1 in 4 people will have flu-like symptoms. These symptoms usually last 2 to 5 days, then go away on their own.
Fewer than 1% of people will have weakness or paralysis in their arms and/or legs. The paralysis can lead to permanent disability and death.
The poliovirus incubation period for nonparalytic symptoms is 3 to 6 days. The onset of paralysis usually occurs 7 to 21 days after infection.
Acute flaccid paralysis (AFP) is a manifestation of a wide spectrum of clinical diseases. Worldwide, children younger than 15 years are at highest risk of developing polio and some other forms of AFP.
Even without laboratory-documented poliovirus infection, AFP is expected to occur at a rate of at least 1 per 100,000 children annually. It can result from a variety of infectious and noninfectious causes.
Known viral causes of AFP include enterovirus, adenovirus, and West Nile virus. However, AFP caused by these agents is very uncommon in the United States. A study examining AFP in children in California from 1992-1998 found the most common diagnoses were Guillain-Barré Syndrome, unspecified AFP, and botulism.
Adults who had paralytic polio during childhood may develop noninfectious post-polio syndrome (PPS) 15 to 40 years later.
PPS is characterized by slow, irreversible worsening of muscle weakness, often in the muscle groups involved during the original infection. Muscle and joint pain are also common symptoms.
The prevalence and incidence of PPS is unclear. Studies estimate that 25–40% of polio survivors suffer from PPS.
Prevention
Polio vaccine provides the best protection against polio. CDC recommends that children and adults who are unvaccinated or incompletely vaccinated get polio vaccine to protect against polio.
Testing and diagnosis
Rapidly investigating suspected polio cases is critical to identifying possible poliovirus transmission and implementing proper control measures.
The Manual for the Surveillance of Vaccine-Preventable Diseases provides current guidelines for those involved in VPD surveillance and response. Learn more about epidemiologic, clinical, and laboratory investigations of AFP to rule out poliovirus infection.
Case of polio
In July 2022, CDC was notified of a case of polio in an unvaccinated individual from Rockland County, New York. The case was caused by vaccine-derived poliovirus type 2. CDC consulted with the New York State Department of Health on their investigation.
This has not changed CDC's recommendations for polio vaccination. CDC still urges everyone who is not fully vaccinated to complete the polio vaccination series as soon as possible.
Reporting suspected cases
Polio is a reportable condition. Know what to do if you suspect your patient may have a case of polio.
Case definitions
A probable case of polio is defined as an acute onset of flaccid paralysis of one or more limbs with decreased or absent tendon reflexes in the affected limbs, without other apparent cause, and without sensory or cognitive loss.
Paralysis usually begins in the arm or leg on one side of the body (asymmetric) and then moves towards the end of the arm or leg (progresses to involve distal muscle groups). This is described as descending paralysis.
Rule out polio
Many patients with AFP will have a lumbar puncture and analysis of cerebrospinal fluid (CSF) performed as part of their evaluation. Detection of poliovirus in CSF from confirmed polio cases is uncommon. A negative CSF test result cannot be used to rule out polio.
Consider polio in patients with polio-like symptoms, especially if the person:
- Is unvaccinated.
- Is incompletely vaccinated.
- Recently traveled abroad to a place where polio still occurs.
- Was exposed to a person who recently traveled to one of these areas.
Only healthcare workers with evidence of complete polio vaccination should attend to the patient.