CHANGES IN HTLV-I POSITIVE RATES AMONG PREGNANT WOMEN IN OKINAWA PRIOR TO THE EFFECTS OF MEASURES INTRODUCED TO PREVENT VERTICAL TRANSMISSION THROUGH BREAST MILK FEEDING

Objectives: Human T cell leukemia virus type-I (HTLV-I) is a causative agent of human T-cell leukemia and HTLV-I associated myelopathy (HAM/TSP). HTLV-I carriers are often infected vertically, especially via mother's milk. Since 1985, clinical measures have been adopted at a hospital in Okinawa to prevent vertical infections.Methods: We examined HTLV-I antibodies in all of the women (total 11, 506) who gave birth after 24 gestational weeks at a hospital on the Okinawa main island from January 1985 to December 1999.Results: The positive rate among all pregnant women was always higher than that among primipara alone. Both figures decreased over the period studied, but the primiparity rate (36-39%) did not change significantly. The percentage of HTLV-I positive primipara pregnant women among the HTLV-I positive total was close to the primiparity rate from 1985 to 1988, but it was considerably lower than the overall primiparity rate thereafter (22-26%).Conclusions: Preventive measures against HTLV-I infection did not contribute to the decrease in HTLV-I positive mothers before 1999 because these measures were adopted from 1985, and so there must be other reasons for the decrease in HTLV-I positive rate. Further studies on social factors and by year of birth are needed to identify factors influencing HTLV-carrier ratios among pregnant women.