A case-control study of risk factors for seropositivity to human T-Lymphotropic virus type I (HTLV-I) in Jamaica

Background. We investigated behavioural and environmental risk factors for seropositivity to human T-lymphotropic virus type I (HTLV-I). Methods. A nested case-control study of 201 HTLV-I seropositive subjects and 225 age: and sex-matched seronegative controls was performed using questionnaire data from the enrolment visit of a cohort study in 1987-1988. HTLV-I serostatus was confirmed using enzyme-linked immunosorbent assay (ELISA) and Western blot. Results. Among women, the number of lifetime sexual partners (P < 0.05, chi(2) trend) and the number of different men fathering a child by the woman (P < 0.06, chi(2) trend) were associated with HTLV-I seropositivity. Use by the female subject of an intrauterine device (IUD) was associated with an increased risk of seropositivity (odds ratio (OR) = 2.67, 95% confidence interval (CI) : 1.13-6.23); condom use was rare in this population. Among male subjects, a larger number of lifetime sexual partners was also associated with HTLV-I seropositivity (P < 0.05, chi(2) trend). No association was found between HTLV-I seropositivity and educational attainment, income, or occupation. Having been breastfed as a child or receipt of a blood transfusion had elevated but imprecise OR due to very high and low prevalence of the risk factors, respectively. Several variables relating to insect or animal exposure showed no association with HTLV-I seropositivity. Conclusions. These data confirm that heterosexual intercourse is a major route of HTLV-I transmission, but do not support suggestions of insect or environmental vectors.