title: Do age-disparate relationships drive HIV incidence in young women? Evidence from a population cohort in rural KwaZulu-Natal, South Africa.
abstract: BACKGROUND
  Based on ethnographic investigations and mathematical models, older sexual partners are often considered a major risk factor for HIV for young women in sub-Saharan Africa. Numerous public health campaigns have been conducted to discourage young women from relationships with older men. However, longitudinal evidence relating sex partner age disparity to HIV acquisition in women is limited.
  
  
  METHODS
  Using data from a population-based open cohort in rural KwaZulu-Natal, South Africa, we studied 15- to 29-year-old women who were HIV seronegative at first interview between January 2003 and June 2012 (n = 2444). We conducted proportional hazards analysis to establish whether the age disparity of women's most recent sexual partner, updated at each surveillance round, was associated with subsequent HIV acquisition.
  
  
  RESULTS
  A total of 458 HIV seroconversions occurred over 5913 person-years of follow-up (incidence rate: 7.75 per 100 person-years). Age disparate relationships were common in this cohort; 37.7% of women reported a partner 5 or more years older than themselves. The age disparity of women's partners was not associated with HIV acquisition when measured either continuously [hazard ratio (HR) for 1-year increase in partner's age: 1.00, 95% confidence interval (CI): 0.97 to 1.03] or categorically (man ≥5 years older: HR, 0.98; 95% CI: 0.81 to 1.20; man ≥10 years older: HR, 0.98; 95% CI: 0.67 to 1.43). These results were robust to adjustment for known sociodemographic and behavioral HIV risk factors and did not vary significantly by women's age, marital status, education attainment, or household wealth.
  
  
  CONCLUSIONS
  HIV incidence in young women was very high in this rural community in KwaZulu-Natal. Partner age disparity did not predict HIV acquistion. Campaigns to reduce age-disparate sexual relationships may not be a cost-effective use of HIV prevention resources in this setting.
authors.affiliation: *Department of Social and Behavioral Sciences, Harvard School of Public Health, Boston, MA; †Africa Centre for Health and Population Studies, University of KwaZulu-Natal, Mtubatuba, South Africa; ‡Faculty of Medicine, University of Southampton, Southampton, United Kingdom; and §Department of Global Health and Population, Harvard School of Public Health, Boston, MA.
authors.forename: Guy
authors.initials: G
authors.lastname: Harling
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Newell
authors.forename: Frank
authors.initials: F
authors.lastname: Tanser
authors.forename: Ichiro
authors.initials: I
authors.lastname: Kawachi
authors.forename: S V
authors.initials: SV
authors.lastname: Subramanian
authors.forename: Till
authors.initials: T
authors.lastname: Bärnighausen
mesh_terms: D000293:Adolescent; D000328:Adult; D000375:Aging; D015331:Cohort Studies; D005260:Female; D015658:HIV Infections / Q000453:epidemiology* / Q000635:transmission*; D006801:Humans; D015994:Incidence; D008297:Male; D012307:Risk Factors; D012747:Sexual Partners; D013019:South Africa / Q000453:epidemiology; D055815:Young Adult