Academic journal article Bulletin of the World Health Organization

Epidemiology and Clinical Characteristics of Acute Flaccid Paralysis Associated with Non-Polio Enterovirus Isolation: The Experience in the Americas

Academic journal article Bulletin of the World Health Organization

Epidemiology and Clinical Characteristics of Acute Flaccid Paralysis Associated with Non-Polio Enterovirus Isolation: The Experience in the Americas

Article excerpt

Introduction

In 1985 the Pan American Health Organization (PAHO) adopted as a goal the interruption of transmission of wild poliovirus in the Americas by 199 (1).(a) The central strategies for attaining this goal were as follows: reaching and maintaining high coverage levels with oral poliovirus vaccine (OPV); strengthening poliomyelitis surveillance; and initiating active outbreak control measures for all reported cases (2,3). National surveillance systems were developed to enable authorities to detect cases of acute flaccid paralysis (AFP) and to apply standardized case investigations for classification.

Because the processing of stool specimens to identify wild poliovirus is crucial for monitoring the success of the programme, a laboratory network for viral isolation was developed by PAHO.(b) Stool specimens collected from AFP patients are processed and the results reported as follows: negative for any enterovirus; positive for wild poliovirus; positive for Sabin-strain poliovirus; positive for non-polio enterovirus (NPEV); or positive for Sabin-strain poliovirus and NPEV. All AFP cases from which wild poliovirus is isolated are automatically confirmed as poliomyelitis. Cases lacking a wild poliovirus isolate are classified as either poliomyelitis or not poliomyelitis according to their clinical presentation, epidemiological evaluation, and laboratory results.

Since NPEVs circulate commonly throughout the world. isolation of an NPEV could represent naturally occurring background viral circulation and. therefore, not be proof of a causal relationship with the paralysis (4). Thus. the isolation of a NPEV from AFP cases does not determine their final classification. The typing of NPEV for purpose of poliomyelitis eradication was not considered useful. since a causal relationship could not be assumed. Nevertheless, NPEVS have been isolated fro cases associated with both paralytic disease an with outbreaks that have clinically mimicked polio myelitis. e.g., coxsackievirus type A7 and enterovirus 71 (5-9).

Reports of NPEV causing poliomyelitis-like illness could have implications for poliomyelitis eradication. For example, the presence of such cases could result in needless outbreak vaccination control activities. Conceivably, resources might be needed to develop the laboratory capability to characterize all NPEV isolates from AFP cases and to quantify the probability of causality.

We conducted a study that had the following objectives: description of the epidemiology of AFP cases with NPEV isolates; characterization of the clinical presentation of AFP cases with NPEV isolates; and comparison of the clinical characteristics of AFP cases with NPEV isolates and those with wild poliovirus isolates. The aim was to determine whether cases with NPEV isolates can be confused with those with wild poliovirus isolates and to gain a better understanding of the potential importance of the former for poliomyelitis eradication.

Methods

The PAHO regional database (Poliomyelitis Epidemiologic Surveillance System (PESS)) was used to identify all reported AFP cases in children less than 15 years of age in the Americas with onset of paralysis from 1989 to 1991. In Latin America, AFP is a notifiable disease and each country reports all AFP cases weekly to PAHO. Country case reports include information on clinical presentation, demographic details, and stool specimen results. All stool specimens from AFP cases are tested for viral isolation in accordance with WHO recommendations.(c) Isolates are reported as negative or positive for NPEV and/or poliovirus. Most countries in the Americas have conducted national immunization days during which OPV has been administered, resulting in frequent isolation of Sabin-strain poliovirus; therefore, polioviruses are further characterized as wild or Sabin-strain by the regional reference laboratory.(d)

We characterized AFP cases with NPEV isolates by age. …

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