Intimate partner violence, relationship power inequity, and incidence of HIV infection in young women in South Africa: a cohort study

Background Cross-sectional studies have shown that intimate partner violence and gender inequity in relationships are associated with increased prevalence of HIV in women. Yet temporal sequence and causality have been questioned, and few HIV prevention programmes address these issues. We assessed whether intimate partner violence and relationship power inequity increase risk of incident HIV infection in South African women. Methods We did a longitudinal analysis of data from a previously published cluster-randomised controlled trial undertaken in the Eastern Cape province of South Africa in 2002-06. 1099 women aged 15-26 years who were HIV negative at baseline and had at least one additional HIV test over 2 years of follow-up were included in the analysis. Gender power equity and intimate partner violence were measured by a sexual relationship power scale and the WHO violence against women instrument, respectively. Incidence rate ratios (IRRs) of HIV acquisition at 2 years were derived from Poisson models, adjusted for study design and herpes simplex virus type 2 infection, and used to calculate population attributable fractions. Findings 128 women acquired HIV during 2076 person-years of follow-up (incidence 6.2 per 100 person-years). 51 of 325 women with low relationship power equity at baseline acquired HIV (8.5 per 100 person-years) compared with 73 of 704 women with medium or high relationship power equity (5.5 per 100 person-years); adjusted multivariable Poisson model IRR 1-51, 95% CI 1.05-2.17, p=0.027. 45 of 253 women who reported more than one episode of intimate partner violence at baseline acquired HIV (9.6 per 100 person-years) compared with 83 of 846 who reported one or no episodes (5.2 per 100 person-years); adjusted multivariable Poisson model IRR 1.51, 1.04-2-21, p=0.032. The population attributable fractions were 13.9% (95% CI 2.0-22-2) for relationship power equity and 11.9% (1.4-19.3) for intimate partner violence. Interpretation Relationship power inequity and intimate partner violence increase risk of incident HIV infection in young South African women. Policy, interventions, and programmes for HIV prevention must address both of these risk factors and allocate appropriate resources.