Academic journal article Bulletin of the World Health Organization

Screening of Cases of Acute Flaccid Paralysis for Poliomyelitis Eradication: Ways to Improve Specificity

Academic journal article Bulletin of the World Health Organization

Screening of Cases of Acute Flaccid Paralysis for Poliomyelitis Eradication: Ways to Improve Specificity

Article excerpt

The Pan American Health Organization in 1985 adopted an initiative to eradicate poliomyelitis from the Western Hemisphere. In 1990, over 2000 cases of acute flaccid paralysis (AFP) were reported in this region, of which <1% were determined to be caused by wild poliovirus. At present, the eradication programme uses AFP as the criterion for surveillance of children aged <15 years; this is 100% sensitive, but not specific. To minimize unnecessary diagnostic investigations, we studied all 4333 cases of AFP reported to the programme during 1989 and 1990 in order to develop more efficient operational screening criteria for cases of AFP.

Among children with AFP, the use of criteria such as age <6 years and either presence of fever at the onset of paralysis or a <4-day period for complete development of paralysis resulted in a sensitivity of 96% (95% C.I. 90-103%) and specificity of 49% (C.I. 47-52%). With criteria of age <6 years and fever present at the onset of paralysis the sensitivity was 75% (C.I. 61-89%) and specificity was 73% (C.I. 71-75%). These results suggest that by screening young children with AFP who either had fever at the onset or showed a rapid progression of paralysis, the number of cases of AFP requiring investigation can be reduced by one half, with minimal compromise in the sensitivity of confirmed poliomyelitis case detection.

Introduction

In September 1985, the Pan American Health Organization officially adopted the initiative to eradicate the transmission of indigenous wild poliovirus transmission from the Region of the Americas[1]. In 1986, when aggressive surveillance activities for acute flaccid paralysis (AFP) were first implemented, 930 clinically confirmed poliomyelitis cases were reported in the Americas. By 1988, with improvements in laboratory technology and support, 32 of the 340 cases of AFP confirmed as poliomyelitis were determined to be associated with wild poliovirus isolation[2, 3]. Between January and October 1991, six poliomyclitis cases in the Region were found to be associated with wild poliovirus isolation. This tremendous decrease in the number of confirmed cases occurred despite a doubling in the number of reported cases of acute flaccid paralysis, from 1000 in 1985 to >2000 estimated by the end of 1991.

The challenge to eradicate the transmission of wild poliovirus from the Americas, and ultimately from the world, to a large extent depends on how well we can distinguish "true" poliomyelitis cases, i.e., those caused by wild poliovirus, from cases of AFP due to other causes. Unlike smallpox, which had a characteristic rash of clinical infection and scar of previous vaccination, poliomyelitis has a wide range of clinical presentations that requires skilled examiners and an extensive laboratory support system for diagnosis[4].

Every new case of AFP detected initiates a costly, labour-intensive chain of events that may include containment measures, such as house-to-house immunization campaigns, clinical follow-up to monitor the progression and type of disease, and complex diagnostic laboratory procedures to determine the etiologic agent.(a) In 1990, less than 1% of the over 2000 cases of AFP reported were confirmed as caused by wild poliovirus. To minimize inefficient use of the limited resources available for global eradication of poliomyelitis, operational screening criteria that maintain sensitivity, but achieve higher specificity are needed so that case-investigation efforts can focus on the cases most likely to be due to poliovirus.(b) To that end, the objective of this study was to develop operational screening criteria which can be applied in the field with more efficient use of the limited global resources.

Methods

Acute flaccid paralysis is a reportable condition in all countries of Latin America. All such cases in children less than 15 years of age that were reported to the Ministries of Health in Latin American countries from January 1989 to December 1990 were enrolled in this study. …

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