Seroindeterminate patterns and seroconversions to human T-lymphotropic virus type I positivity in blood donors from Martinique, French West Indies

BACKGROUND: Screening for human T-lymphotropic virus type I (HTLV-I) antibo dies in volunteer blood donors has been systematic in the French West Indie s since 1989. Western blot-indeterminate results are commonly obtained. The significance of these indeterminate serologic patterns in HTLV-l-endemic a reas is still unclear. STUDY DESIGN AND METHODS: During a 2-year period, 9759 blood donors were te sted for HTLV-I antibodies. The epidemiologic features of HTLV-I-seropositi ve, -seroindeterminate, and -seronegative donors were compared. A lookback investigation was performed for the HTLV-l-seropositive donors, and the HTL V-I-seroindeterminate individuals were followed up. RESULTS: Thirty-nine donors (0.4%) were HTLV-I seropositive and 49 (0.5%) w ere seroindeterminate. The age and sex ratio characteristics of the seroind eterminate donors are divergent from those of the HTLV-I-seropositive group and are more like those of the seronegative population. However, during th e study period, three cases of seroconversion after an initial seroindeterm inate profile were reported. Two cases were detected through follow-up of 3 8 HTLV-I-seroindeterminate donors over a mean of 8 months (2-24 months). Th e third seroconverter belonged to the HTLV-l-seropositive group and was ide ntified through lookback investigation. This case is atypical, with p19 rea ctivity for several months before HTLV-I seropositivity. CONCLUSION: These findings indicate that, although HTLV-I-seroindeterminate donors mainly are HTLV-I-noninfected, the rate of seroconversion in a repe at blood donor population from an endemic region must be taken into conside ration. Moreover, the case of delayed seroconversion observed in this study suggests the difficulty of counseling seroindeterminate blood donors in en demic regions.