Case-control study of factors associated with human T-cell leukemia virus type I infection in southern Miyazaki, Japan.

Abstract

An unusual age- and sex-specific distribution and a remarkably restricted geographic seroprevalence characterize human T-cell leukemia virus type I (HTLV-I) infection. Although the transmission routes of HTLV-I are known, these seroepidemiologic features cannot be fully explained. This study was designed to identify potential characteristics associated with HTLV-I infection in a highly endemic Japanese community. We evaluated occupational, residential, dietary, and medical histories in a case-control study conducted in two neighboring villages in southeastern Miyazaki Prefecture. One hundred forty-four case subjects and 276 control subjects, frequency matched by age, sex, and village, were interviewed. Village-specific profiles of demographic determinants of HTLV-I seroprevalence were generated using multiple logistic regression. Although a different pattern of factors was found for each village, occupations of the subjects and their fathers were associated with HTLV-I infection in both communities--farming in village A and fishing and farming in village B. For village A, there was more than a twofold association both with residence in the township for 55 years or more and with living in a particular area within the village. In addition, case subjects were more likely to have a mother who was deceased (odds ratio = 1.7; 95% confidence interval = 0.96-2.9). HTLV-I infection is characterized by a high degree of microepidemicity in this population, with seroprevalence related to both sociologic and geographic determinants. Moreover, as carriers' mothers themselves have a higher probability of being HTLV-I positive, an increased mortality among those infected with the virus is suggested.