[Seroepidemiological investigation on Japanese encephalitis in Taiwan (January 1989-December 1991)]

The hemagglutination inhibition (HI) test was used to detect sero-confirmed cases of clinically suspected Japanese encephalitis. The results revealed a total of 76 sero-confirmed cases; 24, 27 and 25 cases respectively for the year 1989, 1990 and 1991. The percentages of sero-confirmed cases with respect to reported cases were 12.97%, 12.33%, 10.04% respectively. The mean percentage was 11.64%. The mean number of sero-confirmed cases in recent three years was 25, and morbidity rate per 100,000 population was 0.125. The number of sero-confirmed cases in 1970 was 269, and morbidity rate per 100,000 was 1.86. The comparison of these two groups showed the ratio of 1:11 and 1:15. It demonstrated that the period of 50% sero-conversion of HI antibody positive pigs appeared two months earlier in the middle of May currently as against the middle of July during the years 1966-1968. The period of JE prevalence likewise shifted two months earlier to the months of May, June and July, with a peak in June in 1989-1991 as against the months of July, August and September with a peak in August in 1966-1968. There occurred a few sporadic cases in other months away from the period of major epidemic. With regard to the geographical distribution of the sero-confirmed cases in recent three years, most JE cases were detected in the Taipei basin and the Kaohsiung-Pingtung river basin. The next numerous cases were found in the terrace which extends from Taoyuan, Hsinchu and Miaoli to the central Taiwan and in the Chiayi-Tainan plain. Only four cases were reported from Ilan, Hualien and Taitung counties. During the years between 1955 and 1967, the vast majority of cases occurred among children, especially of 2-9 years of age. The next suffered group was the age group of 10-14 years. In the meanwhile, the current major group of victim was the age group of 10-14 years and its morbidity rate per 100,000 population was 0.30. The second suffered group was the age group of 20-24 years and its morbidity rate was 0.28, and the third was the age group of 0-9 years and its morbidity rate was 0.16. The percentages of sero-confirmed cases of the above each age group with respect to all sero-confirmed cases were 23.68%, 21.05%, 22.36% respectively.(ABSTRACT TRUNCATED AT 400 WORDS)