Ruling Out Poliovirus in Cases of Acute Flaccid Paralysis

Jane Seward, MBBS, MPH


August 04, 2014

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Hello. I'm Dr. Jane Seward. a medical epidemiologist at the Centers for Disease Control and Prevention (CDC). I'm speaking with you as part of the CDC Expert Commentary Series on Medscape.


Although poliovirus is no longer endemic in the United States, there is always the possibility that it could be imported. That's why it is important to exclude poliovirus infection in clinically compatible, unexplained cases of acute flaccid paralysis (AFP), to ensure that any case of poliomyelitis is quickly identified and investigated.

I will provide background on polio epidemiology as well as an overview of AFP and how to rule out polio in cases of unexplained AFP. I will conclude with a review of polio vaccination recommendations for people traveling to countries with ongoing polio transmission.

Before use of the polio vaccine, poliomyelitis was an epidemic disease worldwide, including the United States and other developed countries. Epidemics of increasing magnitude occurred during the first half of the 20th century. In 1952, more than 20,000 cases of polio with permanent paralysis were reported in the United States alone. After the introduction of effective polio vaccines -- first the inactivated poliovirus vaccine (IPV) in 1955, and then the oral poliovirus vaccine (OPV) starting in 1961 -- the reported incidence of polio declined dramatically.

No cases of wild-type polio have been acquired in the United States since 1979. The last imported case of wild-type polio was in 1993. However, we continue to vaccinate our nation's children, knowing that the disease is still found in other parts of the world and could easily be brought into the United States from countries where wild-type poliovirus is circulating. During the past year, 10 countries have had active transmission of wild-type poliovirus. In the past 10 years, at least 40 polio-free countries have been affected through international travel.

Acute Flaccid Paralysis

AFP is the manifestation of a wide spectrum of clinical diseases and is not nationally notifiable in the United States. Worldwide, children under 15 years of age are at highest risk of developing polio and some other forms of AFP.

Even in the absence of 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 245 children under 15 years of age in California from 1992 to 1998 found that the most common diagnoses were Guillain-Barré syndrome (23%), unspecified AFP (21%), and botulism (12%).[1]

Consider Polio

When presented with a case of unexplained AFP, it is important to rule out poliomyelitis. A probable case of polio is defined as an acute onset of a flaccid paralysis of 1 or more limbs with decreased or absent tendon reflexes in the affected limbs, without other apparent cause and without sensory or cognitive loss.[2] Paralysis is usually asymmetric, begins in proximal extremities, and progresses to involve distal muscle groups. This is described as "descending paralysis."

Although AFP with decreased or absent tendon reflexes accounts for only a small proportion of AFP cases, these cases can be challenging to distinguish at initial clinical presentation.

Consider polio in patients presenting with polio-like symptoms, especially if the person is unvaccinated and has recently traveled abroad to a place where polio still occurs, or was exposed to a person who recently traveled from such an area.

If you suspect polio:

Promptly isolate the patient to avoid disease transmission;

Immediately report the suspected case to the health department. A confirmed paralytic poliomyelitis case needs to be reported to CDC within 4 hours of meeting notification criteria; and

Obtain specimens for diagnostic testing for poliovirus detection (polymerase chain reaction [PCR]), viral isolation, and intratypic differentiation as early in the course of illness as possible, including 2 stool specimens and 2 throat swab specimens at least 24 hours apart, ideally within 14 days of symptom onset.

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, and a negative CSF test result cannot be used to rule out polio.[2]

The rapid investigation of suspected polio cases is critical to identifying possible poliovirus transmission and implementing proper control measures. Rapid investigation of suspected cases will allow collection of specimens for poliovirus isolation, which is critical for confirming whether a case of paralytic polio is the result of wild-type or vaccine-related poliovirus infection. For more information, see the CDC poliomyelitis guidelines for epidemiologic, clinical, and laboratory investigations of AFP to rule out poliovirus infection.[3]

Polio is vaccine-preventable. For recommendations on vaccination, including for travel, see the resources listed on this page.

Web Resources

CDC Poliomyelitis Guidelines

CDC. Interim CDC Guidance for Polio Vaccination for Travel to and From Countries Affected by Wild Poliovirus. MMWR Morb Mortal Wkly Rep. 2014;63:591-594

Health Service Executive, Health Protection Surveillance Centre: Acute Flaccid Paralysis (AFP) Surveillance -- What Is It and Why Are We Doing It?

Dr. Jane Seward obtained her medical degree from the University of Western Australia, her clinical training in pediatrics and infectious diseases at Tulane University, and her MPH in Epidemiology from Emory University. Her public health career has spanned both the domestic and international arenas in the fields of maternal and child health, birth defects, nutrition, and immunizations. The main focus of her work at CDC has been domestic vaccine programs, with particular emphasis on measles, mumps, rubella, varicella, and herpes zoster. She has also provided technical assistance to countries on a variety of vaccine program issues, including measles outbreaks, introduction of new vaccines, and routine EPI. She is an internationally recognized varicella and immunization policy expert. Dr. Seward is currently Deputy Director in the Division of Viral Diseases, National Center for Immunizations and Respiratory Diseases, CDC.