A neglected risk factor in HIV transmission, and implications for prevention

There is a greatly increased risk of HIV transmission during receptive anal intercourse (AI) compared to receptive vaginal intercourse (VI). If AI is commonly practised between men and women (heterosexual AI) it may substantially contribute to the spread of HIV epidemics. Heterosexual AI is, however, frequently overlooked as a risk factor and is incompletely understood. In order to assess the contribution of heterosexual AI to HIV epidemics we must first better understand who is engaging in AI, at what frequency, with whom, whether condoms are used, and whether once initiated, the practice is continued throughout the life course. This thesis aims to address these research gaps, using a variety of epidemiological approaches. Systematic reviews and meta-analyses of heterosexual AI practice among young people, South Africans and female sex workers are conducted, as well as data analysis of a cross-sectional survey of Swazi female sex workers and longitudinal analysis of a large, on-going cohort study of U.S. women. Overall, the analyses in this thesis point to heterosexual AI being an integral part of many people’s sexual practice, which often occurs in the context of sexual and physical violence, is associated with heavy drinking and drug use, having multiple partners and unprotected sex. It appears to be as likely practised with casual partners as steady partners and to be more likely condom unprotected than VI practice. Other than a sub-group who practise AI throughout the life course, it appears that most who practise AI do so sporadically and discontinue the practice with age. PrEP may be a suitable to prevent HIV infection in sub-groups who practise AI as a routine part of their sexual practice. Public health messages should emphasise the importance of condom use during AI as well as VI, as the transmission risk during AI is underestimated by many.Open Acces