HIV Transmission in a Declining African Epidemic

Background: Novel HIV prevention interventions such as long-acting pre-exposure prophylaxis (PrEP) could substantially reduce HIV transmission in Africa. However, efficient implementation in high-prevalence settings where incidence has declined requires an understanding of the contemporary dynamics driving new infections. Methods: We identified incident HIV cases from a longitudinal, population-based cohort in Uganda. We individually matched cases to HIV-negative controls; traced and enrolled reported sexual partners; and enrolled female sex workers (FSWs) from reported venues. Conditional logistic regression, transmission modeling, and phylogenetics were used to characterize transmission networks. Findings: From 2021-2024, 38,899 HIV tests among 22,255 people identified 187 people with incident infections (47.6% male); 164 (88%) were enrolled and matched to 164 HIV-negative controls. Overall, 593 non-sex-worker partners (371 enrolled,62.6%), 146 FSW partners (21 enrolled,14.4%), and 28 venues (208 FSWs enrolled) were reported. Incident infection was most strongly predicted by partnership with a FSW (odds ratio:15.5; 95%CI:3.7-64.8), identified in 43.0% of male cases versus 6.3% of controls. Men with FSW partners had larger sexual networks than men without (median:6 vs 2 partners), and 91.2% of men with FSW partners also had non-sex-worker partners. Transmission modeling attributed 34.4% (95%CI:31.5-36.8%) of all male infections and 80.0% (95%CI:73.2-84.4%) of infections among male clients to sex with FSWs. Oral PrEP use among HIV-negative partners of incident cases was low (8.9% in women; 2.1% in men). Interpretation: Men with FSW partners accounted for a substantial share of incident HIV infections and had markedly higher odds of infection than men without such partnerships. Together with the high potential for onward transmission within male client networks, these findings suggest that inclusion of male clients in long-acting HIV prevention strategies could be highly efficient and impactful. Funding: National Institutes of Health, United States; Gates Foundation; National Health and Medical Research Council, Australia.