TUPED765

Title

Mediators of the relationship between transactional sex and incident HIV infection among young women in South Africa enrolled in HPTN 068

Presenter

Marie Stoner

Authors

M. Ranganathan¹, K. Kilburn^2,3, M. Stoner⁴, J.P. Hughes^5,6, C. Macphail^7,8,9, F.X. Gomez-Olive^9,10, K. Kahn^9,10, A. Pettifor^9,11

Institutions

¹London School of Tropical Medicine and Hygiene, London, United Kingdom, ²University of North Carolina at Chapel Hill, Chapel Hill, United States, ³George Washington University, Milken School of Public Health, Washington, DC, United States, ⁴University of North Carolina, Chapel Hill, Chapel Hill, United States, ⁵University of Washington, Seattle, United States, ⁶Statistical Center for HIV/AIDS Research and Prevention (SCHARP), Seattle, United States, ⁷University of Wollongong, School of Health and Society, Wollongong NSW, Australia, ⁸University of the Witwatersrand, Wits Reproductive Health and HIV Institute, Johannesburg, South Africa, ⁹University of the Witwatersrand, Johannesburg, South Africa, MRC/Wits Rural Public Health and Health Transitions Research Unit (Agincourt), School of Public Health, Faculty of Health Sciences, Johannesburg, South Africa, ¹⁰INDEPTH Network, Accra, Ghana, ¹¹University of North Carolina at Chapel Hill, Department of Epidemiology, Chapel Hill, United States

Background: Transactional sex is associated with an increased risk of HIV in adolescent girls and young women, but the mechanism for this relationship is unknown. We hypothesize that young women who report transactional sex may have multiple partners and older partners, thereby increasing their risk of HIV acquisition.
Methods: We used data from the HIV Prevention Trials Network (HPTN) 068 study in rural South Africa. Adolescent girls and young women aged 13-20 years at enrollment were followed approximately annually for up to 6 years. We use the parametric g-formula to estimate the total effect of time varying, frequent transactional sex (receipt of gifts/money at least weekly vs monthly or less) on incident HIV infection and the controlled direct effect for mediation in a simulated cohort of 10,000. The controlled direct effect represents the effect of frequent transactional sex on HIV not operating through partner age difference (>=5 years) and number of sexual partners. We calculated hazard ratios over the study period. Confidence intervals were calculated using the standard deviation of results from 200 bootstrap samples.
Results: We explored scenarios where all young women had multiple partners and where they had only older partners and examined how this would change the effect of frequent transactional sex on incident HIV. In scenarios where girls had only older partners and when they had multiple partners, the controlled direct effect of transactional sex on HIV was attenuated from the total effect, thereby showing mediation. The hazard ratio for the total effect was 1.89 (95% CI: 1.71, 2.06), compared to 1.29 (95% CI: 1.20, 1.39) when holding both partner age and partner number constant.
Conclusions: Both partner age difference and partner number mediate the relationship between transactional sex and incident HIV infection. This suggests that young females with multiple partners serve as a network to high-risk male partners that might render them vulnerable to HIV. However, while these behaviors explain a large portion of the effect of transactional sex on HIV infection, they do not explain the entire effect, indicating that other mediators may also be important.

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