The Epidemiology of Japanese Encephalitis Virus on Taiwan in 1961 *

Abstract

Summary A study of the most severe epidemic of Japanese encephalitis in recent years occurring on the island of Taiwan has been presented. The entire north and central portions of the Island, plus an administrative district at the southern end, were areas of high incidence of the disease. The over-all attack rate in 1961 was 7.15 per 100,000 population as compared with 2.91 for 1960 and 6.0 for the entire 5-year period of 1955–1959. The overall case fatality rate, however, was lower than during previous years. More than one-half of the total cases were reported between 11 July and 10 August 1961. Serological confirmation of the disease was first obtained in June and, during the course of the epidemic, was obtained from almost all administrative areas. The last serologically confirmed case occurred in early October, although sporadic cases were reported through early November. A higher percentage of clinically diagnosed cases of encephalitis were confirmed as JE by a four-fold rise in the hemagglutination-inhibition (HI) test (43%) than by the complement-fixation (CF) test (18%) in this study due to the earlier time of collection of convalescent sera. Single serum specimens with HI titers of 1:160 or greater or with CF titers of 1:16 or greater were considered presumptively positive for JE based on evidence presented in the text above.