RESUMEN
Transactional sex increases sub-Saharan African women's risk of HIV acquisition. We quantitatively explored the pathways contributing towards women's future engagement in transactional sex with casual partners and khwapheni (secret concurrent sex partners). We conducted secondary data analysis from a cluster randomised controlled trial in urban informal settlements in eThekwini Municipality., South Africa. Data were collected at enrolment (t0) and 24 months' later (t2) using self-completed questionnaires. Structural equation modelling (SEM) assessed pathways leading to transactional sex over two years. 677 women 18-35 years were enrolled and 80.5% (n = 545) were followed up. At t2, 44.6% of respondents reported transactional sex with a casual partner or khwapheni. The SEM demonstrated a small effect (d = 0.23) between transactional sex at t0 and at t2. Controlling for past transactional sex, main partner relationship control had a large effect size on future transactional sex (d = 0.60). Hazardous drinking had a medium effect size (d = 0.45) and food insecurity a small effect (d = 0.24), (RMSEA 0.03, 90%CI 0.02-0.04; CFI 0.97; TLI 0.96). HIV prevention programming should highlight current transactional sex but also address structural issues predicting future transactional sex, including food insecurity and alcohol misuse. Gender transformative interventions to reduce controlling behaviours in main relationships are worth investigating.