We systematically reviewed reports about determinants of HIV infection in injecting drug users from 2000 to 2009, classifying findings by type of environmental influence. We then modelled changes in risk environments in regions with severe HIV epidemics associated with injecting drug use. Of 94 studies identified, 25 intentionally examined risk environments. Modelling of HIV epidemics showed substantial heterogeneity in the number of HIV infections that are attributed to injecting drug use and unprotected sex. We estimate that, during 2010-15, HIV prevalence could be reduced by 41% in Odessa (Ukraine), 43% in Karachi (Pakistan), and 30% in Nairobi (Kenya) through a 60% reduction of the unmet need of programmes for opioid substitution, needle exchange, and antiretroviral therapy. Mitigation of patient transition to injecting drugs from non-injecting forms could avert a 98% increase in HIV infections in Karachi; whereas elimination of laws prohibiting opioid substitution with concomitant scale-up could prevent 14% of HIV infections in Nairobi. Optimisation of effectiveness and coverage of interventions is crucial for regions with rapidly growing epidemics. Delineation of environmental risk factors provides a crucial insight into HIV prevention. Evidence-informed, rights-based, combination interventions protecting IDUs' access to HIV prevention and treatment could substantially curtail HIV epidemics.

In sub-Saharan Africa, young women ages 15-24 have more than twice the risk of acquiring HIV as their male counterparts. A growing body of epidemiological evidence suggests that the practice of "transactional sex" may contribute to this disparity. Over the last 15 years, the social sciences have contributed significantly to understanding the meaning of and motivations for this practice. The findings from these studies are rich, but varied, rendering lessons difficult to navigate for intervention and further research. We therefore contribute a historically-grounded, comprehensive literature review on the nature and motivations for women's participation in transactional sex in sub-Saharan Africa. Drawing from over 300 studies (through 2014), we distill three prominent paradigms observed in the literature that we review toward presenting a unified conceptualization of the practice. "Sex for basic needs," the first paradigm, positions women as victims in transactional sexual relationships, with implications for interventions that protect girls from exploitation. In contrast, the "sex for improved social status" paradigm positions women as sexual agents who engage in transactional sex toward attaining a middle-class status and lifestyle. Finally, a third paradigm, "sex and material expressions of love," draws attention to the connections between love and money, and the central role of men as providers in relationships. We find important commonalities in the structural factors that shape the three paradigms of transactional sex including gender inequality and processes of economic change. We suggest that there are three continua stretching across these paradigms: deprivation, agency, and instrumentality. This review proposes a definition of transactional sex and discusses implications for research and interventions aiming to reduce young women's risk of HIV through such relationships. We consider the consequences of drawing from too narrow an understanding of the practice, and highlight the benefits of a broader conceptualization.

IntroductionYoung women aged 15 to 24 years in sub-Saharan Africa continue to be disproportionately affected by HIV. A growing number of studies have suggested that the practice of transactional sex may in part explain women's heightened risk, but evidence on the association between transactional sex and HIV has not yet been synthesized. We set out to systematically review studies that assess the relationship between transactional sex and HIV among men and women in sub-Saharan Africa and to summarize the findings through a meta-analysis.MethodsThe search strategy included 8 databases, hand searches in 10 journals, and searches across 17 websites and portals for organizations as informed by expert colleagues. A systematic review of cross-sectional and longitudinal studies was carried out for studies on women and men who engage in transactional sex published up through 2014. Random effects meta-analysis was used to further examine the relationship between transactional sex and prevalent HIV infection across a subset of studies with the same exposure period. Analyses were conducted separately for men and women.ResultsNineteen papers from 16 studies met our inclusion criteria. Of these 16 studies, 14 provided data on women and 10 on men. We find a significant, positive, unadjusted or adjusted association between transactional sex and HIV in 10 of 14 studies for women, one of which used a longitudinal design (relative risk (RR)=2.06, 95% confidence interval (CI): 1.22 –3.48). Out of 10 studies involving men, only 2 indicate a positive association between HIV and transactional sex in unadjusted or adjusted models. The meta-analysis confirmed general findings from the systematic review (unadjusted meta-analysis findings are significant for women (n=4; pooled odds ratio (OR)=1.54, 95% CI: 1.04–2.28; I2=42.5%, p=0.156), but not for men (n=4; pooled OR=1.47, 95% CI: 0.85–2.56; I2=50.8%, p=0.107).ConclusionsTransactional sex is associated with HIV among women, whereas findings for men were inconclusive. Given that only two studies used a longitudinal approach, there remains a need for better measurement of the practice of transactional sex and additional longitudinal studies to establish the causal pathways between transactional sex and HIV.

Evidence suggests rapid diffusion of injecting drug use and associated outbreaks of HIV among injecting drug users (IDUs) in the Russian Federation and Eastern Europe. There remains a need for research among non-treatment and community-recruited samples of IDUs to better estimate the dynamics of HIV transmission and to improve treatment and health services access. We compare two sampling methodologies Brespondent-driven sampling^(RDS) and chain referral sampling using Bindigenous field workers^(IFS) to investigate the relative effectiveness of RDS to reach more marginal and hard-to-reach groups and perhaps to include those with the riskiest behaviour around HIV transmission. We evaluate the relative efficiency of RDS to recruit a lower cost sample in comparison to IFS. We also provide a theoretical comparison of the two approaches. We draw upon nine community-recruited surveys of IDUs undertaken in the Russian Federation and Estonia between 2001 and 2005 that used either IFS or RDS. Sampling effects on the demographic composition and injecting risk behaviours of the samples generated are compared using multivariate analysis. Our findings suggest that RDS does not appear to recruit more marginalised sections of the IDU community nor those engaging in riskier injecting behaviours in comparison with IFS. RDS appears to have practical advantages over IFS in the implementation of fieldwork in terms of greater recruitment efficiency and safety of field workers, but at a greater cost. Further research is needed to assess how the practicalities of implementing RDS in the field compromises the requirements mandated by the theoretical guidelines of RDS for adjusting the sample estimates to obtain estimates of the wider IDU population.