title: Transmission networks and risk of HIV infection in KwaZulu-Natal, South Africa: a community-wide phylogenetic study.
abstract: The 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.
  
  
  
  We did a cross-sectional household survey of randomly selected individuals aged 15-49 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 ≥90% and genetic distance ≤4·5%).
  
  
  
  From 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 25-40 years, 40·3% in 1548 men aged 25-40 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 25-40 years, and five (8·3%) were aged 41-49 years: mean age difference 8·7 years (95% CI 6·8-10·6; p<0·0001). For the 92 possible phylogenetically linked pairings with the 56 women aged 25-40 years, the age difference dropped to 1·1 years (95% CI -0·6 to 2·8; p=0·111). 16 (39·0%) of 41 probable male partners linked to women younger than 25 years were also linked to women aged 25-40 years. Of 79 men (mean age 31·5 years) linked to women younger than 40 years, 62 (78·5%) were unaware of their HIV-positive status, 76 (96·2%) were not on antiretroviral therapy, and 29 (36·7%) had viral loads of more than 50 000 copies per mL.
  
  
  
  Sexual partnering between young women and older men, who might have acquired HIV from women of similar age, is a key feature of the sexual networks driving transmission. Expansion of treatment and combination prevention strategies that include interventions to address age-disparate sexual partnering is crucial to reducing HIV incidence and enabling Africa to reach the goal of ending AIDS as a public health threat.
  
  
  
  President's Emergency Program for AIDS Relief, US Centers for Disease Control and Prevention, South African Medical Research Council, and MAC AIDS Fund.
authors.affiliation: Centre for the AIDS Programme of Research in South Africa (CAPRISA), Durban, South Africa; University of KwaZulu-Natal, Durban, South Africa; Africa Centre for Population Health, Hlabisa, South Africa.
authors.forename: Tulio
authors.initials: T
authors.lastname: de Oliveira
authors.affiliation: Centre for the AIDS Programme of Research in South Africa (CAPRISA), Durban, South Africa; University of KwaZulu-Natal, Durban, South Africa. Electronic address: ayesha.kharsany@caprisa.org.
authors.forename: Ayesha B M
authors.initials: AB
authors.lastname: Kharsany
authors.affiliation: University of KwaZulu-Natal, Durban, South Africa.
authors.forename: Tiago
authors.initials: T
authors.lastname: Gräf
authors.affiliation: Epicentre, Durban, South Africa.
authors.forename: Cherie
authors.initials: C
authors.lastname: Cawood
authors.affiliation: Epicentre, Durban, South Africa.
authors.forename: David
authors.initials: D
authors.lastname: Khanyile
authors.affiliation: Centre for the AIDS Programme of Research in South Africa (CAPRISA), Durban, South Africa.
authors.forename: Anneke
authors.initials: A
authors.lastname: Grobler
authors.affiliation: National Institute for Communicable Diseases, Johannesburg, South Africa.
authors.forename: Adrian
authors.initials: A
authors.lastname: Puren
authors.affiliation: Global Clinical and Virology Laboratory, Durban, South Africa.
authors.forename: Savathree
authors.initials: S
authors.lastname: Madurai
authors.affiliation: Centre for the AIDS Programme of Research in South Africa (CAPRISA), Durban, South Africa; University of KwaZulu-Natal, Durban, South Africa.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Baxter
authors.affiliation: Centre for the AIDS Programme of Research in South Africa (CAPRISA), Durban, South Africa; University of KwaZulu-Natal, Durban, South Africa; Department of Epidemiology, Columbia University, New York, NY, USA.
authors.forename: Quarraisha Abdool
authors.initials: QA
authors.lastname: Karim
authors.affiliation: Centre for the AIDS Programme of Research in South Africa (CAPRISA), Durban, South Africa; University of KwaZulu-Natal, Durban, South Africa; Department of Epidemiology, Columbia University, New York, NY, USA.
authors.forename: Salim S Abdool
authors.initials: SS
authors.lastname: Karim
mesh_terms: D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D005191:Family Characteristics; D005260:Female; D005838:Genotype; D006678:HIV / Q000276:immunology / Q000302:isolation & purification; D015483:HIV Antibodies / Q000097:blood; D015658:HIV Infections / Q000453:epidemiology* / Q000276:immunology / Q000635:transmission* / Q000821:virology; D006801:Humans; D008875:Middle Aged; D010802:Phylogeny; D015995:Prevalence; D012307:Risk Factors; D012423:Rural Health; D012737:Sex Factors; D012725:Sexual Behavior; D012747:Sexual Partners; D013019:South Africa / Q000453:epidemiology; D011795:Surveys and Questionnaires; D019562:Viral Load; D055815:Young Adult
chemical_list: D015483:HIV Antibodies