Field trial of a Japanese encephalitis diagnostic kit.

Serum and cerebrospinal fluid (CSF) obtained from patients in rural Thailand during an encephalitis epidemic were assayed with a Japanese encephalitis rapid diagnosis kit. Japanese encephalitis was diagnosed by detection of virus-specific IgM (JEV IgM) in CSF (1:10 dilution) or serum (1:100 dilution) with an antibody capture enzyme-linked immunosorbent assay. Specimens were assayed immediately on site at the provincial hospital and scored by visual examination within 4 h. Each specimen was retested carefully later to accurately determine its activity (units) at a single screening dilution; each was tested also at serial dilutions to determine its end-point titer. On-site kit results showed close agreement with subsequent laboratory results for detection and quantitation of JEV IgM and JEV IgG in either serum or CSF. Using the kit on site, admission CSF from 35 (73%) of 48 laboratory-proven JEV-infected patients were scored as definitely positive for JEV IgM, while all 17 CSF specimens from non-JEV infected patients were read as negative (sensitivity 73%, specificity 100%). A rapid and early diagnosis of acute Japanese encephalitis can be accomplished almost anywhere.