Prevalences of HTLV-1 infection and associated risk determinants in an urban population in Guinea-Bissau, West Africa

Objective: To assess the prevalence and modes of transmission of HTLV-1 infection in an adult population in Bissau, and to evaluate possible interactions between the pattern of spread of HTLV-1 and HIV-1/HIV-2. Design and Methods: Univariate and multivariate analyses were used to evaluate gender- and age-specific HTLV-1 prevalences as well as associated risk determinants in an adult population based on a serosurvey comprising 2127 individuals from 304 randomly selected houses in Bissau. Results: Using stringent Western blot criteria, the overall seroprevalence of HTLV-1 was 3.6%, 2.2% among men and 4.7% among women, respectively. One individual was seropositive to HTLV-2. The prevalence of HTLV-1, which increased with age in both genders, however more markedly among women, was >4 times higher (9.4%) among older individuals (>44 years of age) than among younger individuals (2.4%). Blood transfusion and HIV-2 seropositivity were independently associated with HTLV-1 seropositivity in men. Among women, both HIV-2 seropositivity and HIV-1 seropositivity were significant risk determinants. Having had sexual partners was associated with a fivefold increased risk among women but did not reach significance. Conclusion: The adult population of Guinea-Bissau has a higher prevalence of HTLV-1 than reported from most other countries in West Africa. The gender- and age-specific pattern of spread of HTLV-1 closely resembles that observed for HIV-2, another retrovirus prevalent to the region. The close correlation between HTLV-1 and HIV-2 most likely reflects the shared risk factors related to sexual behavior. The implication of the high percentage of double infections in this population needs to be determined.