Prediction of HIV acquisition among men who have sex with men.

OBJECTIVE: To develop and validate an easy-to-use prediction model for HIV acquisition among men who have sex with men (MSM).
METHODS: We developed prediction models using medical records data from an STD clinic (2001-2008) and validated these models using data from the control arm of Project Explore, an HIV prevention trial (1999-2003).
RESULTS: Of 1903 MSM who tested for HIV more than once in the development sample, 101 acquired HIV over 6.7 years of follow-up. Annual HIV incidence was 2.57% (95% confidence interval [CI]: 2.09%, 3.12%). During 4 years of follow-up of 2081 Project Explore control arm participants, 144 acquired HIV for an incidence of 2.32% (95% CI: 1.96%, 2.73%). A prediction model that included variables indicating use of methamphetamine or inhaled nitrites in the prior 6 months, unprotected anal intercourse with a partner of positive or unknown HIV status in the prior year, > or =10 male sex partners in the prior year, and current diagnosis or history of bacterial sexually transmitted infection was well calibrated overall (expected-observed ratio = 1.01; 95% CI: 0.97, 1.05) and had modest discriminatory accuracy at 1 year (area under the receiver-operator characteristic curve = 0.67; 95% CI: 0.60, 0.75) and at 4 years (area under the receiver-operator characteristic curve = 0.66; 95% CI: 0.61, 0.71). Over 4 years, cumulative incidence ranged from 3.9% to 14.3% for groups of men defined by the prediction model.
CONCLUSIONS: A new risk score was predictive of HIV acquisition and could assist providers in counseling MSM and in targeting intensified prevention to MSM at greatest risk for HIV infection. Its accuracy requires further evaluation.