Joint effects of alcohol consumption and high-risk sexual behavior on HIV seroconversion among men who have sex with men

To estimate the effects of alcohol consumption and number of unprotected receptive anal intercourse partners on HIV seroconversion while appropriately accounting for time-varying confounding. Prospective cohort of 3725 HIV-seronegative men in the Multicenter AIDS Cohort Study between 1984 and 2008. Marginal structural models were used to estimate the joint effects of alcohol consumption and number of unprotected receptive anal intercourse partners on HIV seroconversion. Baseline self-reported alcohol consumption was a median 8 drinks/week (quartiles: 2, 16), and 30% of participants reported multiple unprotected receptive anal intercourse partners in the prior 2 years. Five hundred and twenty-nine HIV seroconversions occurred over 35 ,870 person-years of follow-up. After accounting for several measured confounders using a joint marginal structural Cox proportional hazards model, the hazard ratio for seroconversion associated with moderate drinking (1-14 drinks/week) compared with abstention was 1.10 [95% confidence limits: 0.78, 1.54] and for heavy drinking (>14 drinks/week) was 1.61 (95% confidence limits: 1.12, 2.29) (P for trend