Lancet HIV

BackgroundThe incidence of HIV infection in young women in Africa is very high. We did a large-scale community-wide phylogenetic study to examine the underlying HIV transmission dynamics and the source and consequences of high rates of HIV infection in young women in South Africa.MethodsWe did a cross-sectional household survey of randomly selected individuals aged 15\u201349 years in two neighbouring subdistricts (one urban and one rural) with a high burden of HIV infection in KwaZulu-Natal, South Africa. Participants completed structured questionnaires that captured general demographic, socioeconomic, psychosocial, and behavioural data. Peripheral blood samples were obtained for HIV antibody testing. Samples with HIV RNA viral load greater than 1000 copies per mL were selected for genotyping. We constructed a phylogenetic tree to identify clusters of linked infections (defined as two or more sequences with bootstrap or posterior support 6590% and genetic distance 644.5%).FindingsFrom June 11, 2014, to June 22, 2015, we enrolled 9812 participants, 3969 of whom tested HIV positive. HIV prevalence (weighted) was 59.8% in 2835 women aged 25\u201340 years, 40.3% in 1548 men aged 25\u201340 years, 22.3% in 2224 women younger than 25 years, and 7.6% in 1472 men younger than 25 years. HIV genotyping was done in 1589 individuals with a viral load of more than 1000 copies per mL. In 90 transmission clusters, 123 women were linked to 103 men. Of 60 possible phylogenetically linked pairings with the 43 women younger than 25 years, 18 (30.0%) probable male partners were younger than 25 years, 37 (61.7%) were aged 25\u201340 years, and five (8.3%) were aged 41\u201349 years: mean age difference 8.7 years (95% CI 6.8\u201310.6; p