Does per‐act HIV‐1 transmission risk through anal sex vary by gender? An updated systematic review and meta‐analysis

Abstract

Quantifying HIV-1 transmission risk per act of anal intercourse (AI) is important for HIV-1 prevention. We updated previous reviews by searching Medline and Embase to 02/2018. We derived pooled estimates of receptive AI (URAI) and insertive AI (UIAI) risk unprotected by condoms using random effects models. Subgroup analyses were conducted by gender, study design, and whether antiretroviral treatment (ART) had been introduced by the time of the study. Two new relevant studies were identified, one of which met inclusion criteria, adding three new cohorts and increasing number of individuals/partnerships included from 1869 to 14,277. Four studies, all from high-income countries, were included. Pooled HIV-1 risk was higher for URAI (1.25%,95%CI 0.55–2.23%,N=5,I2=87%) than UIAI (0.17%,95%CI 0.09–0.26%,N=3,I2=0%). The sole heterosexual URAI estimate (3.38%,95%CI 1.85–4.91%), from a study of 72 women published in a peer-reviewed journal, was significantly higher than the MSM pooled estimate (0.75%,95%CI 0.56–0.98%,N=4,p<0.0001) and higher than the only other heterosexual estimate identified (0.4%,95%CI 0.08–2.0%, based on 59 women, excluded for being a pre-2013 abstract). Pooled per-act URAI risk varied by study design (retrospective-partner studies: 2.56%,95%CI 1.20–4.42%,N=2 (one MSM, one heterosexual); prospective studies: 0.71,95%CI 0.51–0.93%,N=3 MSM, p<0.0001). URAI risk was lower for studies conducted in the ART era (0.75%,95%CI 0.52–1.03%) than pre-ART (1.67%,95%CI 0.44–3.67%) but not significantly so (p=0.537). Prevention messages must emphasise that HIV-1 infectiousness through AI remains high, even in the ART era. Further studies, particularly among heterosexual populations and in resource-limited settings, are required to elucidate whether AI risk differs by gender, region and following population-level ART scale-up.

Sexually transmitted infections and HIV in the era of antiretroviral treatment and prevention: the biologic basis for epidemiologic synergy

“…Rectal mucosa is a vulnerable tissue and unprotected anal intercourse has the greatest risk for HIV acquisition . Rectal mucosa is thin and friable and heavily defended against infection, thereby enriched with cells receptive to HIV.…”

“…HIV is primarily a sexually transmitted infection (STI) . A single sexual encounter between an HIV‐positive partner and an HIV‐negative partner (a serodifferent/serdiscordant couple) has a low probability of HIV transmission . When transmission occurs, a single viral variant (the transmitted founder virus) is detected 80% of the time, and usually only a maximum of two or three viral variants are transmitted .…”

“…When transmission occurs, a single viral variant (the transmitted founder virus) is detected 80% of the time, and usually only a maximum of two or three viral variants are transmitted . The transmission of HIV is generally relatively inefficient, and predicted to require hundreds of exposures in the case of penile‐vaginal intercourse and dozens of exposures for penile‐rectal exposure .…”

Longitudinal Event-Level Analysis of Gay and Bisexual Men’s Anal Sex Versatility: Behavior, Roles, and Substance Use

“…These results reflect both biology and behavior. Overall, receptive anal sex has a higher probability of infection than insertive anal sex (Baggaley, White, & Boily, 2010;Meng et al, 2015;Baggaley et al, 2018). Beyrer et al (2012, p. 368] succinctly outline the consequences of this differential for versatility, "Role reversal in MSMs, whereby individuals practice both insertive and receptive roles, helps HIV spread by overcoming the low transmission rates from receptive to insertive partners".…”

Childhood Traumatic Experiences and Receptive Anal Intercourse Among Women

“…In 2016, women accounted for approximately 20% of new HIV cases in the country; about 80% of these were attributed to heterosexual sexual contact . Receptive intercourse, both vaginal and anal, results in a higher risk of HIV infection than does insertive intercourse, and receptive anal intercourse (RAI) confers the greatest risk on the male or female receptive partner . Compared with the vagina, the anus is more vulnerable to abrasions during sex, which facilitates infection transmission, and anal mucosa lacks immune barriers to protect against infection .…”