Seroincidence of HIV-1 infection in African women of reproductive age: a prospective cohort study in Kigali, Rwanda, 1988-1992

Abstract

Objective: To estimate the seroincidence of HIV-1 infection among women of reproductive age in Kigali, Rwanda.

Design: Fixed prospective cohort followed for 36 months between November 1988 and June 1992, as part of an ongoing study of mother-to-child transmission of HIV-1.

Setting: Centre Hospitalier, Kigali, Rwanda.

Subjects: A total of 216 HIV-seronegative women were enrolled at delivery between November 1988 and June 1989.

Methods: A blood sample was obtained at delivery to test for HIV antibodies (by enzyme-linked immunosorbent assay and Western blot). Serum was tested every 3 months during follow-up. Incidence density rates of HIV seroconversion were estimated.

Results: The follow-up rate after 3 years was 89%, assessed by the maximum person-years method. The seroincidence density rate was 3.5 per 100 women-years (95% confidence interval, 1.9-5.0). It decreased linearly from 7.6 during the first 6-months postpartum to 2.5 per 100 women-years during the last 6 months of the third year of follow-up. Maternal age did not affect HIV incidence rates. We examined the role of the cohort, counselling, and the first 6-month postpartum effects on this estimate.

Conclusion: This fixed cohort provided an overall estimation of the HIV infection incidence rate and its dynamics. These figures could be used for programming future HIV preventive vaccine efficacy trials in Rwanda.

PIP: The objective was to estimate the seroincidence of HIV-1 infection among women of reproductive age in Kigali, Rwanda. A fixed prospective cohort followed a total of 216 HIV-seronegative women for 36 months between November 1988 and June 1992 at Centre Hospitalier, Kigali, Rwanda. A study of mother-to-child transmission of HIV-1 has been going on at the Centre Hospitalier de Kigali since November 1988. A group of HIV-seronegative women matched by maternal age and parity was consecutively selected as a comparison group. The mean maternal age was 25.1 years (SD, 4.5 years), and the total number of pregnancies was 2.7 (SD, 1.8). A blood sample was obtained at delivery to test for HIV antibodies (by enzyme-linked immunosorbent assay and Western blot). Serum was tested every 3 months during follow-up. The follow-up rate after 3 years was 89.2% (577/646.75), assessed by the maximum person-years method. 20 seroconversions were documented during the first 36 months of follow-up among the 216 women seronegative at inclusion, yielding a cumulative incidence of 11.2%. The largest number of seroconversions (8/20; 40%) was observed in the first 6 months of the postpartum period. The seroincidence density rate was 3.5/100 women-years (95% confidence interval, 1.9-5.0). It decreased linearly from 7.6 during the first 6-months postpartum to 2.5 per 100 women-years during the last 6 months of the third year of follow-up (P = 0.01). Maternal age did not affect HIV incidence rates. We examined the role of the cohort, counseling, and the first 6-month postpartum effects on this estimate. The study confirms that pregnant women may represent a population in which the HIV seroincidence is high and concentrated in the immediate postpartum period. Pregnant women should become a potential target group for future large scale vaccination trials and programs with adequate follow-up. These figures could be used for programming future HIV preventive vaccine efficacy trials in Rwanda.