[Seroepidemiological study of rubella in Thailand]

The epidemiology of rubella in Thailand was studied by measuring the HI antibodies in 2,798 human serum samples collected in 1977 and from 1982 through 1986. In the study of the Meo and Karen hill tribes and employees of the Raming Tea Plantation living in high land in 1977, high antibody-negative rates against rubella were observed among young children aged 14 or less, so that the antibody was assumed to have been acquired by most of the people aged 15 or over. However, the antibody level in those aged 15 or older differed from group to group. Employees of a tobacco factory and students at a high school in Sarapij were studied. Only two of the 54 employees had the negative antibody. The geometric mean antibody titers were as high as log2 7.081 and 7.058, respectively, which suggested an epidemic of rubella close to the time the specimens were collected. The antibody levels of patients with complaints other than rubella were compared between Chiang Mai and Bangkok in 1977. No significant difference was observed between the two cities in the 20 to 24 years age group but the antibody-negative rate was higher in Bangkok than in Chiang Mai. Serum samples collected from children in the Comprehensive Child Care Clinic, Chiang Mai University, in 1982, 1984 and 1985 were tested for their antibody levels to rubella. The age by which the subject children had naturally acquired the antibody was lower in 1982 than in 1985. The antibody-negative rate of outpatients in Chiang Mai University Hospital in 1985 was definitely higher than that in 1977, and that in 1977 was lower than that of adults in Chiang Mai in 1983 to 1986. These data would suggest that a severe epidemic of rubella prevailed in the Chiang Mai district before 1977, but the disease was not common during the eight subsequent years. Our data in Thailand were compared with records in Japan in 1976. In Japan the antibody-negative rate decreased with age and it was lower than 5% in adults aged 30 years or more. Conversely, in Thailand the antibody-negative rate decreased by 20 to 24 years of age but it was still more than 25% after 25 years of age. The geometric mean antibody titre of the antibody-positive people decreased with age in Japan, but in Thailand it was as high as log2 6.33, even in adults of 30 or more years of age.