Per-act HIV transmission risk during anal sex may be higher than previously thought

Estimating per-act HIV transmission risk: a systematic review.

Patel P, Borkowf CB, Brooks JT, Lasry A, Lansky A, Mermin J. AIDS. 2014 Jun 19;28(10):1509-19. doi: 10.1097/QAD.0000000000000298.

Background: Effective HIV prevention programs rely on accurate estimates of the per-act risk of HIV acquisition from sexual and parenteral exposures. We updated the previous risk estimates of HIV acquisition from parenteral, vertical, and sexual exposures, and assessed the modifying effects of factors including condom use, male circumcision, and antiretroviral therapy.

Methods: We conducted literature searches to identify new studies reporting data regarding per-act HIV transmission risk and modifying factors. Of the 7 339 abstracts potentially related to per-act HIV transmission risk, three meta-analyses provided pooled per-act transmission risk probabilities and two studies provided data on modifying factors. Of the 8 119 abstracts related to modifying factors, 15 relevant articles, including three meta-analyses, were included. We used fixed-effects inverse-variance models on the logarithmic scale to obtain updated estimates of certain transmission risks using data from primary studies, and employed Poisson regression to calculate relative risks with exact 95% confidence intervals for certain modifying factors.

Results: Risk of HIV transmission was greatest for blood transfusion, followed by vertical exposure, sexual exposures, and other parenteral exposures. Sexual exposure risks ranged from low for oral sex to 138 infections per 10 000 exposures for receptive anal intercourse. Estimated risks of HIV acquisition from sexual exposure were attenuated by 99.2% with the dual use of condoms and antiretroviral treatment of the HIV-infected partner.

Conclusion: The risk of HIV acquisition varied widely, and the estimates for receptive anal intercourse increased compared with previous estimates. The risk associated with sexual intercourse was reduced most substantially by the combined use of condoms and antiretroviral treatment of HIV-infected partners.

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Editor’s notes: The study updates the 2005 Centres for Disease Control (CDC) per-act HIV transmission risks with estimates from recent publications. In addition, it summarizes the effects of various co-factors that modify the transmission risks during sexual exposure. These include genital ulcer disease, viral load, disease stage, use of antiretrovirals, condom use and male circumcision. However, estimates from low-income countries on sexual and mother-to-child transmission are very heterogeneous and not included in the analyses. In general, the updated estimates of transmission risks are comparable to figures from the 2005 CDC study. But they also suggest that the transmission probabilities for both receptive and insertive anal intercourse could be higher than previously thought. Further, the study reasserts that the per-act risk for all sexual exposures is substantially attenuated through the use of condoms and antiretrovirals. These new estimates will be important for both modelling studies and prevention programmes. But a better understanding of HIV transmission risks in low-income countries is needed. 

Asia, Northern America, Oceania
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