Rubella HI antibody among pregnant women in Amami. Oshima Islands

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Oshima Shoto consists of 5 islands and has a population of 183 thousands. These islands are located in the southern end of Japan and stretch to Ryukyu under U. S. administration (population: 914 thousands) where we found that more than 360 patients with rubella syndrome were born after the malignant rubella epidemic in 1964-1965. Whereas only 10 patients with rubella syndrome were found in Oshima, though there had been rubella epidemis in 1965 and 1966. In order to find out the reason why there was a great difference in the epidemic of rubella syndrome between Oshima and Ryukuu, we tested the serum specimens from a series of pregnant women in Oshima for rubella HI antibody.Serum specimens were obtained from 375 pregnant women in this district for the period March through December in 1969. The age of them ranged from 19 to 44.Rubella HI antibody was detectable in 62% of the serum specimens tested and this indicated 38% of them did not have demonstrable antibody. The frequency of the pregnant women without antibody in the age group 21-30 was 47% and was significantly higher than that of the patients of 31 or older. There was no singificant difference in the frequency of rubella HI antibody among 5 islands studied.Sever, J. L. et al., Rowls, W. E. et al. and Thongcharoen, P. reported the populations of a large number of women without rubella antibody in Hawaii, Jamaica, Trinidad and Thailand. These areas share similar warm climatic condition. Kono, R. pointed out the frequency of the seronegative pregnant women was high in southern Japan as compared with northern Japan. Considering the interruption of rubella epidemic by summer season, the warm climate generally may not be fit for spread of rubella. It can be considered the rubella epidemics in temperate zone such as Oshima and Ryukyu were often small scale and a large number of women were left susceptible to rubella.However, there was a great difference in the epidemic of rubella between Ryukyu and Oshima: the rubella epidemic in Ryukyu in 1964-1965 was very extensive and these in Oshima in 1965 and in 1966 were small scale as usual and many susceptible pregnant women did not have an attack of rubella. Forty seven per cent of the pregnant women in the age group 21-30 in Oshima were regarded to be still at risk for bubella infection.