Poliovirus, Paralytic Poliomyelitis and Nonparalytic Poliovirus Infection
2024 Case Definition

Background

Poliomyelitis is characterized by the acute onset of flaccid paralysis caused by one of the 3 types of polioviruses, whether wild-type or vaccine-associated. Paralysis is typically asymmetrical, often affecting the lower limbs. The majority of poliovirus infections are asymptomatic or subclinical, and fewer than 1% are paralytic. The onset of paralysis is rapid, and usually does not progress after 3 days. Transmission of poliovirus occurs primarily through the fecal-oral route.

Surveillance for acute flaccid paralysis (AFP) has not been routinely conducted in the U.S. since polio was eradicated, but the appearance of a condition with a similar clinical presentation in 2014 led to the development of a standardized case definition for surveillance of acute flaccid myelitis (AFM), which is a subtype of AFP. AFM is characterized by rapid onset of flaccid weakness in one or more limbs and distinct abnormalities of the spinal cord gray matter on magnetic resonance imaging (MRI). To date, all stool specimens from AFM patients tested at CDC have been negative for poliovirus except for the patient from New York in 2022, who initially came to the attention of public health as a suspect AFM patient. The previous definition for a confirmed paralytic poliomyelitis case does not include a laboratory component, thus AFM cases can technically be considered confirmed cases of paralytic poliomyelitis. Therefore, the case definitions for Paralytic Poliomyelitis and Nonparalytic Poliovirus Infection have been revised to help simplify reporting and clarify the difference between AFM and paralytic poliomyelitis.

Clinical Criteria

• Acute onset of flaccid paralysis with decreased or absent tendon reflexes in the affected limbs, in the absence of a more likely alternative diagnosis.

Laboratory Criteria

Confirmatory Laboratory Evidence:

• Poliovirus detected by sequencing of the capsid region of the genome by the CDC Poliovirus Laboratory, OR
• Poliovirus detected in an appropriate clinical specimen (e.g., stool [preferred], cerebrospinal fluid, oropharyngeal secretions) using a properly validated assay^, AND specimen is not available for sequencing by the CDC Poliovirus Laboratory.

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.
^ The Global Polio Laboratory Network (GPLN) provides guidelines on acceptance of results from labs that are not in GPLN; assays would have to be validated and approved by GPLN. CDC is part of GPLN.

Criteria to Distinguish a New Case from an Existing Case

Post-polio syndrome is a condition that can affect survivors of poliovirus infection decades after recovering from their initial infection. A person with post-polio syndrome should not be enumerated as a new case.