Trends in HTLV-1 prevalence and incidence of adult T-cell leukemia/lymphoma in Nagasaki, Japan.

Most previous studies aimed at estimating the number of human T-cell leukemia virus type-1 (HTLV-1) carriers in endemic areas have been based on seroprevalence rates in blood donors; however, this may result in underestimation because of the healthy donor effect. People who have health problem do not donate blood. In the present study, the number of HTLV-1 carriers in Nagasaki City was estimated based on the seroprevalence rates in a hospital-based population from Nagasaki University Hospital. In accordance with previous reports, seroprevalence of HTLV-1 was higher in females, and year of birth-specific seroprevalence showed a significant annual decline in both genders (P for trend: <0.0001). The estimated number of HTLV-1 carriers in Nagasaki City was 36,983. The incidence of adult T-cell leukemia/lymphoma (ATLL) among HTLV-1 carriers was estimated using data from the Nagasaki Prefectural Cancer Registry. The estimated annual incidence of ATLL was 61 per 100,000 HTLV-1 carriers, and the crude lifetime risk of the development was 7.29% for males and 3.78% for females. There is a large pool of HTLV-1 carriers aged over 70 years, and a continuing development of cases of ATLL among the elderly is therefore expected.