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Review
. 2009 Feb;9(2):118-29.
doi: 10.1016/S1473-3099(09)70021-0.

Heterosexual risk of HIV-1 infection per sexual act: systematic review and meta-analysis of observational studies

Marie-Claude Boily  1 , Rebecca F Baggaley, Lei Wang, Benoit Masse, Richard G White, Richard J Hayes, Michel Alary
Affiliations
Review

Heterosexual risk of HIV-1 infection per sexual act: systematic review and meta-analysis of observational studies

Marie-Claude Boily et al. Lancet Infect Dis. 2009 Feb.

Abstract

We did a systematic review and meta-analysis of observational studies of the risk of HIV-1 transmission per heterosexual contact. 43 publications comprising 25 different study populations were identified. Pooled female-to-male (0.04% per act [95% CI 0.01-0.14]) and male-to-female (0.08% per act [95% CI 0.06-0.11]) transmission estimates in high-income countries indicated a low risk of infection in the absence of antiretrovirals. Low-income country female-to-male (0.38% per act [95% CI 0.13-1.10]) and male-to-female (0.30% per act [95% CI 0.14-0.63]) estimates in the absence of commercial sex exposure (CSE) were higher. In meta-regression analysis, the infectivity across estimates in the absence of CSE was significantly associated with sex, setting, the interaction between setting and sex, and antenatal HIV prevalence. The pooled receptive anal intercourse estimate was much higher (1.7% per act [95% CI 0.3-8.9]). Estimates for the early and late phases of HIV infection were 9.2 (95% CI 4.5-18.8) and 7.3 (95% CI 4.5-11.9) times larger, respectively, than for the asymptomatic phase. After adjusting for CSE, presence or history of genital ulcers in either couple member increased per-act infectivity 5.3 (95% CI 1.4-19.5) times versus no sexually transmitted infection. Study estimates among non-circumcised men were at least twice those among circumcised men. Low-income country estimates were more heterogeneous than high-income country estimates, which indicates poorer study quality, greater heterogeneity of risk factors, or under-reporting of high-risk behaviour. Efforts are needed to better understand these differences and to quantify infectivity in low-income countries.

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Figures

Figure 1
Figure 1
Flowchart summarising results of the search on heterosexual per-act HIV-1 transmission probabilities. The 11 publications rejected on specific criteria consisted in four mathematical modelling studies,,,, two obsolete abstracts,- and five reviews,,-. The 43 publications included 26 publications included in the principle meta-analysis and seven publications only included in the sub-analyses by risk factor,,,,,,. The remaining publications were duplicates and not included in any analysis but are shown in Webonly table 1 for completion.
Figure 2
Figure 2
Forest plots of crude per-act study estimates in the absence of commercial sex exposure for: a) Combined M-to-F and F-to-M estimates; b) F-to-M; and c) M-to-F HIV transmission. The point estimate, sample size (N) and 95%CI for each study are represented. The indice ‘d’ indicates that the 95%CI were derived from available data. The indice “i” indicates that the estimate and CI were derived from information provided in main study; the indice “r” indicates that the original rate estimates and CI were converted into probabilities. For reference, a vertical dotted line is shown at 0·001 because this has previously been a commonly cited value for HIV-1 per-act transmission probability. Light and dark blue lines show estimates from simple prospective and prospective-discordant couple studies, respectively. Green and red lines show estimates from simple retrospective and retrospective-partner studies, respectively. Triangles identify developing country estimates. Circles identify developed country estimates. Note that only the lower bound of the 95%CI of Cameron et al and Satten et al estimates appear on the F-to-M transmission forest plot because they are too large. “L” and “R” denote the prospective-discordant-couple and retrospective-partner-study components of Downs et al, respectively.
Figure 2
Figure 2
Forest plots of crude per-act study estimates in the absence of commercial sex exposure for: a) Combined M-to-F and F-to-M estimates; b) F-to-M; and c) M-to-F HIV transmission. The point estimate, sample size (N) and 95%CI for each study are represented. The indice ‘d’ indicates that the 95%CI were derived from available data. The indice “i” indicates that the estimate and CI were derived from information provided in main study; the indice “r” indicates that the original rate estimates and CI were converted into probabilities. For reference, a vertical dotted line is shown at 0·001 because this has previously been a commonly cited value for HIV-1 per-act transmission probability. Light and dark blue lines show estimates from simple prospective and prospective-discordant couple studies, respectively. Green and red lines show estimates from simple retrospective and retrospective-partner studies, respectively. Triangles identify developing country estimates. Circles identify developed country estimates. Note that only the lower bound of the 95%CI of Cameron et al and Satten et al estimates appear on the F-to-M transmission forest plot because they are too large. “L” and “R” denote the prospective-discordant-couple and retrospective-partner-study components of Downs et al, respectively.
Figure 2
Figure 2
Forest plots of crude per-act study estimates in the absence of commercial sex exposure for: a) Combined M-to-F and F-to-M estimates; b) F-to-M; and c) M-to-F HIV transmission. The point estimate, sample size (N) and 95%CI for each study are represented. The indice ‘d’ indicates that the 95%CI were derived from available data. The indice “i” indicates that the estimate and CI were derived from information provided in main study; the indice “r” indicates that the original rate estimates and CI were converted into probabilities. For reference, a vertical dotted line is shown at 0·001 because this has previously been a commonly cited value for HIV-1 per-act transmission probability. Light and dark blue lines show estimates from simple prospective and prospective-discordant couple studies, respectively. Green and red lines show estimates from simple retrospective and retrospective-partner studies, respectively. Triangles identify developing country estimates. Circles identify developed country estimates. Note that only the lower bound of the 95%CI of Cameron et al and Satten et al estimates appear on the F-to-M transmission forest plot because they are too large. “L” and “R” denote the prospective-discordant-couple and retrospective-partner-study components of Downs et al, respectively.
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