title: The risk of HIV transmission within HIV-1 sero-discordant couples appears to vary across sub-Saharan Africa.
abstract: BACKGROUND
  Representative and precise estimates for the annual risk of HIV transmission (ϕ) from the infected to the uninfected partner in a stable HIV-1 sero-discordant couple (SDC) are not available. Nevertheless, quantifying HIV infectiousness is critical to understanding HIV epidemiology and implementing prevention programs.
  
  
  METHODS
  We estimated ϕ and examined its variation across 23 countries in sub-Saharan Africa (SSA) by constructing and analyzing a mathematical model that describes HIV dynamics among SDCs. The model was parameterized using empirical measures such as those of the nationally representative Demographic and Health Surveys. Uncertainty and sensitivity analyses were conducted to assess the robustness of the findings.
  
  
  RESULTS
  We estimated a median ϕ of 11.1 per 100 person-years across SSA. A clustering based on HIV population prevalence was observed with a median ϕ of 7.5 per 100 person-years in low HIV prevalence countries (<5%) compared to 19.5 per 100 person-years in high prevalence countries (>5%). The association with HIV prevalence explained 67% of the variation in ϕ, and suggested an increase of 0.95 per 100 person-years in ϕ for every 1% increase in HIV prevalence.
  
  
  CONCLUSIONS
  Empirical measures from cohort studies appear to underestimate HIV infectiousness in SSA. The risk of HIV transmission among SDCs appears also to vary across SSA, and this may have contributed to the contrasting HIV epidemic trajectories in this continent.
authors.affiliation: Infectious Disease Epidemiology Group, Weill Cornell Medical College - Qatar, Cornell University, Qatar Foundation - Education City, Doha, Qatar.
authors.forename: Hiam
authors.initials: H
authors.lastname: Chemaitelly
authors.affiliation: Infectious Disease Epidemiology Group, Weill Cornell Medical College - Qatar, Cornell University, Qatar Foundation - Education City, Doha, Qatar.
authors.forename: Susanne F
authors.initials: SF
authors.lastname: Awad
authors.affiliation: Infectious Disease Epidemiology Group, Weill Cornell Medical College - Qatar, Cornell University, Qatar Foundation - Education City, Doha, Qatar; Department of Public Health, Weill Cornell Medical College, Cornell University, New York, NY, USA; Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA. Electronic address: lja2002@qatar-med.cornell.edu.
authors.forename: Laith J
authors.initials: LJ
authors.lastname: Abu-Raddad
mesh_terms: D017954:Africa South of the Sahara / Q000453:epidemiology; D005191:Family Characteristics; D015658:HIV Infections / Q000175:diagnosis / Q000453:epidemiology* / Q000635:transmission*; D018023:HIV Seronegativity; D006679:HIV Seropositivity; D015497:HIV-1 / Q000302:isolation & purification; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D008962:Models, Theoretical; D015995:Prevalence; D018570:Risk Assessment; D012307:Risk Factors; D012747:Sexual Partners
keywords: HIV transmission; Incidence rate; Mathematical model; Sero-discordancy; Sub-Saharan Africa