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- Special edition Epidemiologic characteristics of the 1982 Japanese encephalitis epidemic occurred in Korea
- Joung Soon Kim, In Sook Lee, Hyun Sool Lim, Chu Won Lee, Suk Woo Shin
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Epidemiol Health 1983;5(1):1-28
DOI: https://doi.org/
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Abstract
In 1982, about 2,000 cases of Japanese encephalitis have occurred despite the governmental effort such as the early warning of the increased vector mosquito density, vaccination campaign and other control measures. Japanese encephalitis had been endemic in Korea with small and large epidemics since the JE virus was isolated in 1949; The JE cases had been remarkably reduced to a few hundred cases since 1969 for over a decade, which increased suddely in 1982. In order to identify responsible factors of the epidemic, all reported cases and a part of hospital patients through medical record survey were analysed. Cases suspicious of encephalitis were reported to Ministry of Health and Social Affairs through, national administrative channel and the final confirmation of the disease was based on the HI antiboy titer of which criteria were set up by the government; it was defined as true encephalitis case when the antibody titer was over 1 : 160 and the subsequent tests stowed fourfold increase in case the first test less than 1 : 160. The hospital medical record survey was carried out on 54% of all reported cases. Summary of the study results is as followings: Among 2975 reported cases about 40% of them were confirmed to be true Japanese encephalitis, about 20% were confirmed to be negative serologically, and the rest of the cases reported never been re-test following the first tests that were negative. Accordingly if the same positive rate is applied for the unconfirmed cases, the total true cases of Japanese encephlaitis estimated to be 2,112 cases. When confirmed cases were compared with total reported cases in the date of onset, age and sex specific incidence rate, duration between the first medical attendence and the onset, duration of hospital admission and the type of medical facility utilized, the both groups showed the similar patterns so that it was unable to characterize them separately. Only with the confirmed cases of Japanese encephalitis the incidence rate of the disease was 3.1 per 100,000 population for whole Korean. The incidence rate varied by province from 2.0 in Gangweon to 7.1 in Chungbug Province; in the agricultural rural area the incidence rate was 3 times higher than in metropolitan area being the higher in South-western part of the country than Northeastern part. Also the disease started from the Southwest moving toward the Northeast which coincided with the time of vector mosquito density Peaks. The age specific incidence rates were higher among younger ages between 5 and 15 years and males 1.7 times higher than females. The majority(87%) of the patients had received medical attention within five days from the onset. The duration of hospital admission was 138.5 days. The case fatality rate was 3.3% being Higher among females, and younger children in females and older ages in males. Among total deaths about one third of death occurred within one week and 97% in two weeks. The sero-conversion for the specific antibody by the JE viral infection was found to be so slow that the serological test as the confirmatory evidence was inefficient; The positive conversion occurred in 46% of confirmed cases in one week and 78% in two weeks after the onset of the disease. The human epidemic of Japanese encephalitis showed association with the densities of pigs and vector population when data were comparatively analysed. The medical record survey in which 1692 cases out of 2,975 reported cases were included, showed that only 41% of them were confirmed as true Japanese encephalitis, 5% as non-encephalitis cases and 59% never had follow-up confirmatory test but negative in single serological test. The final diagnosis on discharge varied widely; Japanese encephalitis 32.6%, suspected Japanese encephalitis 6.6%, meningo-encephalitis 6.1%, viral encephalits 3.1%, encephalitis 23.6%, epidemic encephalitis 4.4%, and aseptic meningitis 5.5% which comprised 83% of total cases studied. Also the specific antibody positive rate varied by the final diagnosis ranging from 18% for aseptic meningitis to 62% for epidemic encephalitis. When these diseases were compared with each another in epidemiologic and clinical charateristics, they were very similar except meningo-encephalitis, viral encephalitis and aseptic meningitis that revealed a little differences in many aspects as presented in tables of text. This study was supported by Korean Institute of Population and Health.
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