title: Measuring population transmission risk for HIV: an alternative metric of exposure risk in men who have sex with men (MSM) in the US.
abstract: BACKGROUND
  Various metrics for HIV burden and treatment success [e.g. HIV prevalence, community viral load (CVL), population viral load (PVL), percent of HIV-positive persons with undetectable viral load] have important public health limitations for understanding disparities.
  
  
  RESULTS
  Using data from an ongoing HIV incidence cohort of black and white men who have sex with men (MSM), we propose a new metric to measure the prevalence of those at risk of transmitting HIV and illustrate its value. MSM with plasma VL>400 copies/mL were defined as having 'transmission risk'. We calculated HIV prevalence, CVL, PVL, percent of HIV-positive with undetectable viral loads, and prevalence of plasma VL>400 copies/ml (%VL400) for black and white MSM. We used Monte Carlo simulation incorporating data on sexual mixing by race to estimate exposure of black and white HIV-negative MSM to a partner with transmission risk via unprotected anal intercourse (UAI). Of 709 MSM recruited, 42% (168/399) black and 14% (44/310) white MSM tested HIV-positive (p<.0001). No significant differences were seen in CVL, PVL, or percent of HIV positive with undetectable viral loads. The %VL400 was 25% (98/393) for black vs. 8% (25/310) for white MSM (p<.0001). Black MSM with 2 UAI partners were estimated to have 40% probability (95% CI: 35%, 45%) of having ≥1 UAI partner with transmission risk vs. 20% for white MSM (CI: 15%, 24%).
  
  
  CONCLUSIONS
  Despite similarities in other metrics, black MSM in our cohort are three times as likely as white MSM to have HIV transmission risk. With comparable risk behaviors, HIV-negative black MSM have a substantially higher likelihood of encountering a UAI partner at risk of transmitting HIV. Our results support increasing HIV testing, linkage to care, and antiretroviral treatment of HIV-positive MSM to reduce prevalence of those with transmission risk, particularly for black MSM.
authors.affiliation: Department of Medicine, Emory University, Atlanta, Georgia, United States of America. colleen.kelley@emory.edu
authors.forename: Colleen F
authors.initials: CF
authors.lastname: Kelley
authors.forename: Eli S
authors.initials: ES
authors.lastname: Rosenberg
authors.forename: Brandon M
authors.initials: BM
authors.lastname: O'Hara
authors.forename: Paula M
authors.initials: PM
authors.lastname: Frew
authors.forename: Travis
authors.initials: T
authors.lastname: Sanchez
authors.forename: John L
authors.initials: JL
authors.lastname: Peterson
authors.forename: Carlos
authors.initials: C
authors.lastname: Del Rio
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Sullivan
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D015658:HIV Infections / Q000097:blood / Q000453:epidemiology* / Q000209:etiology* / Q000635:transmission*; D015497:HIV-1 / Q000502:physiology; D018451:Homosexuality, Male; D006801:Humans; D008297:Male; D011153:Population; D015995:Prevalence; D012307:Risk Factors; D012725:Sexual Behavior / Q000502:physiology*; D019562:Viral Load; D055815:Young Adult