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  HIV Research for Prevention
October 21-25, 2018
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HIV Transmission Rate 10 Times Higher With Anal vs Vaginal Sex: Meta-Analysis
  HIV Research for Prevention (HIVR4P), October 21-25, 2018, Madrid
Mark Mascolini
In high-income countries HIV transmission risk stands at least 10 times higher with anal sex than with vaginal sex, according to a 14,000-person meta-analysis [1]. Analyzed studies indicate about a 1.25% per act transmission rate with condomless receptive anal intercourse.
Anal intercourse without condoms propels the HIV epidemic in men who have sex with men (MSM), and many heterosexual couples have anal sex [2]. To update previous work on per-act HIV transmission rate with anal sex, Imperial College London researchers and collaborators at other centers conducted a new systematic review and meta-analysis. They aimed to determine how anal transmission risk varies by type of anal sex, gender, and antiretroviral use.
The investigators searched electronic databases through February 2018 for studies of HIV transmission risk per anal sex act. They used random effects models to pool data on receptive and insertive anal sex, both with and without condoms. Subgroup analyses considered HIV transmission mode (MSM or heterosexual) and whether combination antiretroviral therapy had arrived at the time of the study.
In addition to previously analyzed studies, the Imperial College team identified 1 new study that met inclusion criteria. The new study added 3 cohorts and boosted the number of individuals or partners assessed from under 1870 in previous meta-analyses to 14,277. Altogether, the new analysis considered 4 studies, all from high-income countries. Three studies involved MSM and 1 involved heterosexuals.
The new pooled HIV risk per condom-free receptive anal act stood at 1.25% (95% confidence interval [CI] 0.55 to 2.23), while the pooled risk for condom-free insertive anal act was 0.17% (95% CI 0.09 to 0.26). The single condom-free receptive anal sex study in heterosexuals involved 72 women. Their per-act HIV risk was significantly higher than the pooled risk among MSM (3.38% versus 0.75%, P < 0.0001). The pooled condom-free anal sex per-act risk was lower in studies conducted in the combination ART era than in pre-ART studies, but that difference lacked statistical significance (0.75% versus 1.67%, P = 0.537).
Citing previous research, the investigators estimated that per-act HIV transmission risk is at least 10 times greater with condomless anal than condomless vaginal sex in high-income countries (0.08%, 95% CI 0.06 to 0.11) [3]. They stressed that anal HIV transmission risk seems unaffected by the arrival of potent antiretroviral combinations. And they proposed that HIV prevention messages should stress the high risk of anal HIV transmission.
1. Baggaley RF, Owen BN, Silhol R, et al. Per act HIV transmission risk through anal intercourse: an updated systematic review and meta-analysis. HIV Research for Prevention (HIVR4P), October 21-25, 2018, Madrid. Abstract P28.09.
2. Owen BN, Brock PM, Butler AR, et al. Prevalence and frequency of heterosexual anal intercourse among young people: a systematic review and meta-analysis. AIDS Behav. 2015;19:1338-1360.
3. Boily MC, Baggaley RF, Wang L, et al. Heterosexual risk of HIV-1 infection per sexual act: systematic review and meta-analysis of observational studies. Lancet Infect Dis. 2009;9:118-129.