Estimating per-act HIV transmission risk: a systematic review

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Abstract

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. We conducted literature searches to identify new studies reporting data regarding per-act HIV transmission risk and modifying factors. Of the 7339 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 8119 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. 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. 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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Determinants of per-coital-act HIV-1 infectivity among African HIV-1-serodiscordant couples.

James P Hughes, Jared Baeten, Jairam R. Lingappa … (2012)

Knowledge of factors that affect per-act infectivity of human immunodeficiency virus type 1 (HIV-1) is important for designing HIV-1 prevention interventions and for the mathematical modeling of the spread of HIV-1. We analyzed data from a prospective study of African HIV-1-serodiscordant couples. We assessed transmissions for linkage within the study partnership, based on HIV-1 sequencing. The primary exposure measure was the HIV-1-seropositive partners' reports of number of sex acts and condom use with their study partner. Of 3297 couples experiencing 86 linked HIV-1 transmissions, the unadjusted per-act risks of unprotected male-to-female (MTF) and female-to-male (FTM) transmission were 0.0019 (95% confidence interval [CI], .0010-.0037) and 0.0010 (95% CI, .00060-.0017), respectively. After adjusting for plasma HIV-1 RNA of the HIV-1-infected partner and herpes simplex virus type 2 serostatus and age of the HIV-1-uninfected partner, we calculated the relative risk (RR) for MTF versus FTM transmission to be 1.03 (P = .93). Each log(10) increase in plasma HIV-1 RNA increased the per-act risk of transmission by 2.9-fold (95% CI, 2.2-3.8). Self-reported condom use reduced the per-act risk by 78% (RR = 0.22 [95% CI, .11-.42]). Modifiable risk factors for HIV-1 transmission were plasma HIV-1 RNA level and condom use, and, in HIV-1-uninfected partners, herpes simplex virus 2 infection, genital ulcers, Trichomonas vaginalis, vaginitis or cervicitis, and male circumcision.

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Per-contact probability of HIV transmission in homosexual men in Sydney in the era of HAART.

James Jansson, Fengyi Jin, S Kippax … (2010)

The objective of this study is to estimate per-contact probability of HIV transmission in homosexual men due to unprotected anal intercourse (UAI) in the era of HAART. Data were collected from a longitudinal cohort study of community-based HIV-negative homosexual men in Sydney, Australia. A total of 1427 participants were recruited from June 2001 to December 2004. They were followed up with 6-monthly detailed behavioral interviews and annual testing for HIV till June 2007. Data were used in a bootstrapping method, coupled with a statistical analysis that optimized a likelihood function for estimating the per-exposure risks of HIV transmission due to various forms of UAI. During the study, 53 HIV seroconversion cases were identified. The estimated per-contact probability of HIV transmission for receptive UAI was 1.43% [95% confidence interval (CI) 0.48-2.85] if ejaculation occurred inside the rectum, and it was 0.65% (95% CI 0.15-1.53) if withdrawal prior to ejaculation was involved. The estimated transmission rate for insertive UAI in participants who were circumcised was 0.11% (95% CI 0.02-0.24), and it was 0.62% (95% CI 0.07-1.68) in uncircumcised men. Thus, receptive UAI with ejaculation was found to be approximately twice as risky as receptive UAI with withdrawal or insertive UAI for uncircumcised men and over 10 times as risky as insertive UAI for circumcised men. Despite the fact that a high proportion of HIV-infected men are on antiretroviral treatment and have undetectable viral load, the per-contact probability of HIV transmission due to UAI is similar to estimates reported from developed country settings in the pre-HAART era.