title: Is serosorting effective in reducing the risk of HIV infection among men who have sex with men with casual sex partners?
abstract: BACKGROUND
  We investigated the prevalence and protective value of serosorting [ie, establishing HIV concordance in advance to practice unprotected anal intercourse (UAI)] with casual partners (CP) among HIV-negative men who have sex with men (MSM) using longitudinal data from 2007 to 2011.
  
  
  METHODS
  Men of the Amsterdam Cohort Studies were tested biannually for HIV-1 antibodies and filled in questionnaires about sexual behavior in the preceding 6 months. HIV incidence was examined among men who practiced UAI, UAI with serosorting, or consistent condom use, using Poisson regression.
  
  
  RESULTS
  Of 445 MSM with CPs, 31 seroconverted for HIV during a total follow-up of 1107 person-years. Overall observed HIV incidence rate was 2.8/100 person-years. Consistent condom use was reported in 64%, UAI in 25%, and UAI with serosorting in 11% of the 2137 follow-up visits. MSM who practiced serosorting were less likely to seroconvert [adjusted incidence rate ratio (aIRR) = 0.46; 95% confidence interval (CI): 0.13 to 1.59] than MSM who had UAI, but more likely to seroconvert than MSM who consistently used condoms (aIRR = 1.32; 95% CI: 0.37 to 4.62), although differences in both directions were not statistically significant. MSM who consistently used condoms were less likely to seroconvert than MSM who had UAI (aIRR = 0.37; 95% CI: 0.18 to 0.77).
  
  
  CONCLUSIONS
  The protective effect for serosorting we found was not statistically significant. Consistent condom use was found to be most protective against HIV infection. Larger studies are needed to demonstrate whether serosorting with CPs offers sufficient protection against HIV infection, and if not, why it fails to do so.
authors.affiliation: Public Health Service Amsterdam, Cluster Infectious Diseases, Department of Research, Amsterdam, Netherlands.
authors.forename: Wijnand
authors.initials: W
authors.lastname: van den Boom
authors.affiliation: Public Health Service Amsterdam, Cluster Infectious Diseases, Department of Research, Amsterdam, Netherlands.
authors.forename: Roos
authors.initials: R
authors.lastname: Konings
authors.affiliation: Public Health Service Amsterdam, Cluster Infectious Diseases, Department of Research, Amsterdam, Netherlands.
authors.forename: Udi
authors.initials: U
authors.lastname: Davidovich
authors.affiliation: HIV Center for Clinical and Behavioral Studies, Department of Psychiatry, Columbia University and New York State Psychiatric Institute, New York, NY, USA.
authors.forename: Theo
authors.initials: T
authors.lastname: Sandfort
authors.affiliation: Public Health Service Amsterdam, Cluster Infectious Diseases, Department of Research, Amsterdam, Netherlands.|Department of Infectious Diseases, Tropical Medicine and AIDS, CINIMA, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Maria
authors.initials: M
authors.lastname: Prins
authors.affiliation: Public Health Service Amsterdam, Cluster Infectious Diseases, Department of Research, Amsterdam, Netherlands.
authors.forename: Ineke G
authors.initials: IG
authors.lastname: Stolte
mesh_terms: D000328:Adult; D015331:Cohort Studies; D018562:Disease Transmission, Infectious / Q000517:prevention & control*; D015483:HIV Antibodies / Q000097:blood; D015658:HIV Infections / Q000517:prevention & control* / Q000635:transmission; D059147:HIV Serosorting; D015497:HIV-1 / Q000276:immunology; D018451:Homosexuality, Male; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D009426:Netherlands; D011446:Prospective Studies; D018570:Risk Assessment; D011795:Surveys and Questionnaires
chemical_list: D015483:HIV Antibodies