The association between heterosexual anal intercourse and HIV acquisition in three prospective cohorts of women

Receptive anal intercourse (RAI) may substantially increase HIV acquisition risk per sex act compared to receptive vaginal intercourse (RVI). To understand how levels of RAI change over time and evaluate the impact of exposure definitions for RAI on HIV incidence, we analysed three prospective HIV cohorts of women: RV217, MTN-003 (VOICE), and HVTN 907. At baseline 16.0% (RV 217), 17.5% (VOICE) of women reported RAI in the past 3 months and 27.3% (HVTN 907) in the past 6 months, with RAI declining during follow-up by around 3-fold. Hazard ratios, adjusted for potential confounders (aHR), indicate that reporting RAI at baseline increased HIV incidence in the three cohorts: 1.1 (95% Confidence interval: 0.8-1.5) for VOICE, aHR of 3.3 (1.6-6.8) for RV 217, and 1.9 (0.6-6) for HVTN 907. Using time-varying exposure definition slightly increased the estimated association for VOICE (aHR=1.2; 0.9-1.6), however reporting >30% RAI sex acts during VOICE follow-up was not associated with higher HIV incidence (aHR=0.7 (0.4-1.1)). Women who always reported RAI during follow-up where also at increased HIV acquisition risk. Overall, we found that precisely estimating RAI and HIV association after multiple RVI/RAI exposures is sensitive to RAI exposure definitions and may be influenced by measurement errors.