On-site assessment on the definition and classification of suspected cases in the manual of WHO Japanese Encephalitis Surveillance Standards

Abstract

To assess the new edition of WHO Japanese Encephalitis (JE) Surveillance Standards (WHO Standards) based on syndrome surveillance data and to provide field evidence regarding the standards. Based on syndrome surveillance data, acute encephalitis syndrome (AES) case was categorized, according to the WHO Standards. A cohort study was applied to estimate the AES definition set in the Standard and relative risk was computed to estimate the existence and intensity of statistical correlation between AES and JE cases. Percentage of attributable risk was counted to describe the coverage of AES for JE cases in the studied population. Sensitivity, specificity, Youden index and positive predictive value of AES components were calculated for the purpose of identifying the clinical values under the screening program. 1424 suspected cases were evaluated in the surveillance program and 1396 cases with ELISA result, of which 109 positive cases were detected. According to the "standardized" classification, a total of 706 cases in line with AES case definition, were categorized into 83 cases of JE, 425 cases of AES unknown and 198 cases of AES other agent. In the cohort study, a relative risk of 4.62 (95%CI: 2.80 - 7.63) and the percentage of attributable risk as 78.35% (95%CI: 64.25% - 86.89%) were observed. The AES definition for JE was significantly effecting on the screening programs and a strong correlation strength was observed in the study. AES syndrome could cover most of the JE cases. "Convulsions", with appreciative screening value, was recommended to be involved into the new version of the WHO Standards.