title: The implications of respondent concurrency on sex partner risk in a national, web-based study of men who have sex with men in the United States.
abstract: BACKGROUND
  Men who have sex with men (MSM) represent the largest HIV risk group in the United States. Sexual concurrency catalyzes HIV transmission in populations by increasing the indirect exposure of one's sex partners to one another. Although individual-level (egocentric) designs have demonstrated a high prevalence of concurrency among MSM respondents, methods are lacking for understanding the exposure implications for partners (dyads) reported in such studies.
  
  
  METHODS
  A new technique for manipulating egocentrically collected partnership timing data to measure the degree to which respondents' patterns of concurrency and serial monogamy resulted in the indirect exposure of respondents' partners to other partners was developed. Two outcomes were constructed for each partner: any concurrent or serially monogamous exposure to another partner (any exposure) and any concurrent exposure to another partner, irrespective of serial monogamy (any concurrent exposure). Reports of unprotected anal intercourse (UAI) were incorporated to construct the outcomes of 'any UAI exposure' and 'any concurrent UAI exposure.' This method was applied to an online study of MSM aged ≥18 years, with comparisons made by partner's race-ethnicity, age, type, and meeting location.
  
  
  RESULTS
  Among 4060 repeat partners of 2449 MSM, 73% had any exposure in the previous 6 months; 58% had any concurrent exposure. Among UAI partners, 37% had concurrent UAI exposure. Black UAI partners were more likely than whites to have any concurrent UAI exposure [unadjusted odds ratio (95% confidence interval) = 1.34 (1.05 to 1.70)], as were casual UAI partners relative to main partners [unadjusted odds ratio (95% confidence interval) = 4.37 (3.58 to 5.35)]. In adjusted models, black UAI partners were significantly more likely to have any UAI exposure, but not concurrent UAI exposure. Casual UAI partners remained more exposed by both outcomes.
  
  
  CONCLUSIONS
  Sex partners of MSM, particularly casual and black non-Hispanic partners, face a high degree of exposure to other partners.
authors.affiliation: Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA 30322, USA.
authors.forename: Eli S
authors.initials: ES
authors.lastname: Rosenberg
authors.forename: Richard B
authors.initials: RB
authors.lastname: Rothenberg
authors.forename: David G
authors.initials: DG
authors.lastname: Kleinbaum
authors.forename: Rob B
authors.initials: RB
authors.lastname: Stephenson
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Sullivan
mesh_terms: D000328:Adult; D001741:Black or African American / Q000706:statistics & numerical data*; D016001:Confidence Intervals; D003625:Data Collection; D015658:HIV Infections / Q000635:transmission*; D018451:Homosexuality, Male / Q000208:ethnology*; D006801:Humans; D020407:Internet; D008297:Male; D016017:Odds Ratio; D012307:Risk Factors; D012747:Sexual Partners; D013997:Time Factors; D014481:United States; D047568:Unsafe Sex / Q000208:ethnology; D044465:White People / Q000706:statistics & numerical data*; D055815:Young Adult