Objectives: To compare risk factors for HIV seropositivity with risk factors for HIV seroconversion in a population of volunteer blood donors in Harare, Zimbabwe, and to assess the impact of risk factor exclusion strategies on the safety of the blood supply.
Design: A secondary analysis of a longitudinal cohort study was performed.
Subjects and methods: The subjects were volunteer blood donors who were also taking part in a prospective cohort study in Harare, Zimbabwe. They were tested for HIV antibodies upon enrollment and at 6-month intervals. Their donation history, age, marital status and the presence or absence of multiple sex partners and paying for sex were assessed as predictors of HIV seropositivity and HIV seroconversion. The impact of exclusion strategies on blood safety was modeled by estimating the number of HIV-infected units that would escape detection by antibody screening if blood donors with these risk factors were excluded.
Results: The HIV seroprevalence among persons accepted for blood donation was 8.8%; the HIV seroincidence was 2.1 per 100 person-years. Significant risk factors for HIV seropositivity were being a new donor (odds ratio 7.3, 95% confidence interval 4.4-1 2.1), age over 25 years (odds ratio 1.6, confidence interval 1.1-2.4), being married (odds ratio 1.7, confidence interval 1.2-2.6), paying for sex (odds ratio 2.6, confidence interval 1.7-3.9) and multiple sex partners (odds ratio 2.1, confidence interval 1.4-2.9). Significant risk factors for HIV seroconversion were age under 25 years (hazard ratio 2.5, confidence interval 1.4-5.0) and being unmarried (hazard ratio 2.5, confidence interval 1.4-5.0). Of note, age and marital status reversed their direction of association with respect to HIV seropositivity and HIV seroconversion. Exclusion strategies based on strong predictors of HIV seroconversion were the most effective in improving the safety of the blood supply.
Conclusions: A distinction between risk factors for HIV seropositivity and HIV seroconversion is necessary in order to develop strategies to reduce the residual risk of transfusion-associated HIV transmission. Because window-period donations are the most important source of residual HIV contamination and arise from incident infections, research to develop risk factor exclusion strategies must focus on predictors of HIV seroconversion.
PIP: Secondary analysis of data from a longitudinal cohort study of voluntary blood donors in Harare, Zimbabwe, confirmed a residual risk of HIV contamination of blood due to laboratory false-negatives and donations made during the window period. It further identified different risk factors for prevalent HIV infection (HIV seropositivity) compared with incident HIV (HIV seroconversion). The HIV prevalence rate among the 1515 blood donors enrolled in the study during 1993-95 was 8.8% (2.1 per 100 person-years). HIV seroprevalence was highest among first-time donors, those 21-45 years of age, married persons, those with more than 1 sexual partner in the preceding year, and those who had paid for sex in the past year. Among the 1142 initially HIV-negative donors who had at least 1 6-month follow-up test, there were 40 seroconversions (2.1 per 100 person-years). Significant risk factors for seroconversion were age under 25 years and single marital status. Since window-period donations account for substantially more HIV contamination of the blood supply than laboratory false-negatives, donor exclusion criteria based on risk factors for incident HIV infection are more likely to reduce the residual risk of HIV contamination than exclusion criteria based on risk factors for prevalent HIV infection.