title: HIV serosorting as a harm reduction strategy: evidence from Seattle, Washington.
abstract: OBJECTIVE
  We sought to estimate how serosorting may affect HIV prevalence and individual risk among men who have sex with men in Seattle, Washington, and how the results vary under different assumptions of HIV testing frequency, heterogeneity in sexual behavior, and condom use.
  
  
  METHODS
  We developed a deterministic mathematical model of HIV transmission dynamics. Data from the 2003 random digit dial study of men who have sex with men conducted in Seattle, Washington (n = 400) are used to parameterize the model.
  
  
  RESULTS
  Predicted population-level HIV prevalence as well as an individual's risk of HIV acquisition decreases when the odds of serosorting are increased in the mathematical model. In our model based on observed levels of serosorting, we predict an HIV prevalence of 16%. In contrast, if serosorting were eliminated in the population, we predict that HIV prevalence would increase to 24.5%. However, our findings depend on rates of condom use, mean anal sex contact rates, and HIV testing in the population.
  
  
  CONCLUSIONS
  Under realistic scenarios of sexual behavior and testing frequency for men who have sex with men in the United States, serosorting can be an effective harm reduction strategy.
authors.affiliation: Center for Studies in Demography and Ecology, Box 353412, University of Washington, Seattle, WA 98195, USA. scassels@u.washington.edu
authors.forename: Susan
authors.initials: S
authors.lastname: Cassels
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Menza
authors.forename: Steven M
authors.initials: SM
authors.lastname: Goodreau
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Golden
mesh_terms: D000328:Adult; D017280:Condoms / Q000706:statistics & numerical data; D015658:HIV Infections / Q000453:epidemiology* / Q000517:prevention & control / Q000523:psychology / Q000635:transmission; D015528:HIV Seroprevalence / Q000639:trends*; D040261:Harm Reduction; D018451:Homosexuality, Male; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D015995:Prevalence; D040242:Risk Reduction Behavior; D012309:Risk-Taking; D012725:Sexual Behavior / Q000523:psychology / Q000706:statistics & numerical data*; D014861:Washington / Q000453:epidemiology