Declining Seroprevalence and Transmission of HTLV-I in Japanese Families Who Immigrated to Hawaii

This study examined the seroprevalence and transmission of human T cell lymphotropic virus type I (HTLV-I) in Japanese families who originated in Okinawa, an area in which HTLV-I is endemic, and who were currently residing in Hawaii, a nonendemic area. Among a cohort of Japanese men whose sera were collected in Hawaii in 1967-1975, those of Okinawan ancestry had an HTLV-I seroprevalence of 11.4%. This study, conducted in 1987-1988, sampled 142 index subjects from this male cohort and tested them along with their wives, children, and spouses of the children for HTLV-I antibodies. Seropositivity in their wives was 11.4% and 41.2% among the seronegative and seropositive index subjects, respectively; seropositivity also increased from 29.4% to 35.3% to 58.8% with the husbands' increasing antibody levels by tertiles. Elevated antibody levels may be a marker for infectivity, which is associated with more efficient sexual transmission of HTLV-I. The age-adjusted odds ratio for the association of seropositivity between husband and wife, however, was four times lower than that reported among native Okinawans. In addition, a substantially low seroprevalence (1.3%) was found among their offspring. The decline in HTLV-I transmission in this migrant population may be due to low infectivity in the parent generation who live in a nonendemic environment, increasing numbers of offspring marrying outside of the Okinawan community, and improved living circumstances.