Rates of HIV‐1 Transmission per Coital Act, by Stage of HIV‐1 Infection, in Rakai, Uganda

TLDR

The study estimated HIV‑1 transmission rates per coital act in HIV‑discordant couples by the index partner’s stage of infection. Using a retrospective cohort of 235 monogamous couples in Rakai, Uganda, the authors confirmed transmission via sequence analysis and calculated per‑coital‑act rates stratified by recent seroconversion, early, late, and pre‑death stages. Transmission rates were highest during early infection (0.0082 per act) and decreased thereafter, with higher rates associated with elevated viral load, genital ulcer disease, and younger index partner age.

Abstract

We estimated rates of human immunodeficiency virus (HIV)-1 transmission per coital act in HIV-discordant couples by stage of infection in the index partner.We retrospectively identified 235 monogamous, HIV-discordant couples in a Ugandan population-based cohort. HIV transmission within pairs was confirmed by sequence analysis. Rates of transmission per coital act were estimated by the index partner's stage of infection (recent seroconversion or prevalent or late-stage infection). The adjusted rate ratio of transmission per coital act was estimated by multivariate Poisson regression.The average rate of HIV transmission was 0.0082/coital act (95% confidence interval [CI], 0.0039-0.0150) within approximately 2.5 months after seroconversion of the index partner; 0.0015/coital act within 6-15 months after seroconversion of the index partner (95% CI, 0.0002-0.0055); 0.0007/coital act (95% CI, 0.0005-0.0010) among HIV-prevalent index partners; and 0.0028/coital act (95% CI, 0.0015-0.0041) 6-25 months before the death of the index partner. In adjusted models, early- and late-stage infection, higher HIV load, genital ulcer disease, and younger age of the index partner were significantly associated with higher rates of transmission.The rate of HIV transmission per coital act was highest during early-stage infection. This has implications for HIV prevention and for projecting the effects of antiretroviral treatment on HIV transmission.