HIGH HIV-1 INCIDENCE IN YOUNG-WOMEN MASKED BY STABLE OVERALL SEROPREVALENCE AMONG CHILDBEARING WOMEN IN KINSHASA, ZAIRE - ESTIMATING INCIDENCE FROM SERIAL SEROPREVALENCE DATA

Objective: To describe the dynamics of the HIV-1 epidemic in childbearing women in Kinshasa, Zaire, by estimating incidence from serial seroprevalence studies. Methods: In 1986 and 1989, 5937 and 4623 pregnant women, respectively, were screened for HIV-1 in Kinshasa. We estimated age-specific incidence from two seroprevalence surveys by using a birth-year cohort analysis and adjusting for differences in mortality and fertility between HIV-1-infected and uninfected women. Mortality and fertility data were measured in a cohort of women recruited from the survey in 1986 and followed until 1989. Results: While the overall HIV-1 seroprevalence changed little (5.8% in 1986 and 6.5% in 1989; P=0.17), the prevalence increased in birth-year cohorts of women under 25 years of age in 1989 from 3.2 to 6.2% (P<0.001), but decreased for women above 25 years of age from 6.9 to 6.7% (P=0.7). In addition, new HIV infections between 1986 and 1989 were balanced by a higher mortality and lower fertility observed in HIV-infected women. After adjusting for these effects, we estimated an overall 3-year cumulative HIV-1 incidence of 2.8 per 100 uninfected women [95% confidence interval (Cl), 1.4-4.2]. The highest incidence, 5.7 per 100 (95% Cl, 3.5-8.0), was in women aged 20-24 years in 1989. Conclusion: Despite an overall relatively stable HIV-1 prevalence in childbearing women in Kinshasa between 1986 and 1989, approximately 40% of all HIV-1 infections detected in the 1989 survey occurred between 1986 and 1989, and 60% occurred in women under 25 years of age in 1989.