Trend in Prevalence of Human T-Lymphotropic Virus Type-1 (HTLV-1) Infection in Japanese Blood Donors, Nagasaki, 1999 to 2006.

To evaluate time-trend of HTLV-1 prevalence and the effect of preventative measure against the viral transmission are important in the virus endemic regions. In Nagasaki, Japan, an endemic area of HTLV-1, a routine serological virus screening for blood donors and a prefecture-wide intervention project (the ATL Prevention Program; APP) to prevent milk-borne transmission for the virus carrier mothers have been conducted since 1986 and 1987, respectively. However, the effects of both projects on the virus seroprevalence have not been well evaluated. In this study, we conducted trend analyses of age-specific, birth-year-specific, and period-specific seroprevalence of HTLV-1 for first-time blood donors who donated between January 1999 and December 2006. Among 55668 first-time donors (age at donation; 16–65 years, birth year; 1934–1990), 718 were test positive for HTLV-1, indicating that the overall seroprevalence was1.29% (95%CI, 1.20–1.39). Prevalence was significantly higher in women than men (1.53% vs. 1.13%; OR; 1.36, 95%CI; 1.17–1.57). Seroprevalence increased significantly with increasing age at donation from 0.70% at 16–25 years to 7.34% at over 56 years (Chi-square test, P < 0.0001). The annual prevalence was 1.32 in 1999, 1.31 in 2002, and 1.37 in 2006, indicating that there was no significant secular trend during 1999–2006 (P for trend=0.99). In analyses by age at donation, trends of HTLV-1 prevalence significantly declined among age over 56 years (P for trend=0.02) and age 16–25 years (P for trend=0.0007), whereas in birth-year-specific analyses, there was no apparent change of the prevalence over time, except in birth year 1981–90 group in which the prevalence declined from 1.22% in 1999 to 0.44% in 2006 (P for trend < 0.0001). In analyses for limited birth year from 1985 to 1990, the seroprevalence declined from 0.75% in birth year 1985–86 group, 0.31% in 1987–88 group, to zero% in 1989–90 group (P for trend =0.0002). HTLV-1 seroprevalence was significantly lower among donors born in 1987–90 (after APP) than 1985–86 (before APP). These results indicate that a birth-year-specific analysis for HTLV-1 prevalence may be appropriate to evaluate secular trend since the virus mostly transmit during infancy, and that a prefecture-wide intervention, the refraining from breast-feeding by the virus carrier mothers, contributes a declining HTLV-1 seroprevalence in our region.