Boily MC, Baggaley RF, Wang L, Masse B, White RG, Hayes RJ, Alary MHeterosexual risk of HIV-1 infection per sexual act: systematic review and meta-analysis of observational studies. Lancet Infect Dis 9: 118-129

Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College, London, UK.
The Lancet Infectious Diseases (Impact Factor: 22.43). 03/2009; 9(2):118-29. DOI: 10.1016/S1473-3099(09)70021-0
Source: PubMed


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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    • "This gap is significant given that different types of risk relationships pose different levels of HIV transmission risk (Baggaley, Boily, White, & Alary, 2006; Boily et al., 2009). Although risk compensation in our study was relatively uncommon, results suggest that risk compensation was more likely to occur in what could be considered as less established relationships (i.e., relationships of shorter duration). "
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    ABSTRACT: Formative research into the behavioral factors surrounding HIV vaccine uptake is becoming increasingly important as progress is made in HIV vaccine development. Given that the first vaccines on the market are likely to be partially effective, risk compensation (i.e., increased risk behavior following vaccination) may present a concern. This study characterized the relationships in which HIV vaccine-related risk compensation is most likely to occur using dyadic data collected from people who use drugs, a high-risk group markedly underrepresented in extant literature. Data were collected from 433 drug users enrolled in a longitudinal study in the USA. Respondents were asked to provide the first name and last initial of individuals with whom they had injected drugs and/or had sex during the past six months. For each partner, respondents reported their likelihood of increasing risk behavior if they and/or their partner received an HIV vaccine. Using generalized linear mixed models, relationship-level correlates to risk compensation were examined. In bivariate analysis, risk compensation was more likely to occur between partners who have known each other for a shorter time (odds ratio [OR] = 0.95, 95% confidence interval [CI]: 0.90-0.99, p = 0.028) and between those who inject drugs and have sex together (OR = 2.52, CI: 1.05-6.04, p = 0.039). In relationships involving risk compensation, 37% involved partners who had known each other for a year or less compared to only 13% of relationships not involving risk compensation. Adjusting for other variables, duration (OR: 0.95, CI: 0.90-1.00, p = 0.033) was associated with risk compensation intent. These analyses suggest that risk compensation may be more likely to occur in less established relationships and between partners engaging in more than one type of risk behavior. These data provide further support for the need to expand measures of risk compensation in HIV vaccine preparedness studies to assess not only if people will change their behavior, but also with whom.
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    • "During sexual transmission, HIV-1 viral particles or virus-infected cells have to overcome a series of obstacles to establish a successful infection including: mucus; the integrity of the genital or rectal epithelial barriers; host innate defense mechanisms; and the sparsity, activation state and susceptibility of mucosal CD4 + target cells (Borrow P, et al., 2010; Derdeyn C A, et al., 2004; Keele B F, et al., 2008; Miller C J, et al., 2005; Temchura V, et al., 2014; Tsai L, et al., 2014; Zhang Z Q, et al., 2004). These obstacles collectively result in a relatively low transmission rate per exposure (Boily M C, et al., 2009; Wawer M J, et al., 2005). However, potential selective advantages acquired by HIV-1, such as enhanced binding to specific cell subtypes, might significantly increase the chances of a successful transmission event. "
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    • "The model was parameterised and calibrated to a representative Avahan district, Bellary, with 15.6% HIV prevalence amongst FSWs in 2004 (Appendix S1). Uncertainty ranges were defined for the behavioral parameters using data from the IBBA surveys undertaken amongst FSWs and their clients in Bellary [12], [27]–[28], biological parameters came from the published literature [29]–[31], and data on the scale and intensity of intervention activities came from the intervention monitoring system (MIS) [27]. The number of FSWs reached per year in the typical/representative district was set to be the mean annual number of FSWs reached in each district (1429 FSWs) over 2004–2007. "
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