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Background:

HIV incidence in the United States among men who have sex with men (MSM) has been increasing since 2000, and MSM remain the most heavily impacted risk group in the US HIV epidemic.

Methods:

We modeled HIV transmissions, using data from MSM in five US cities from the National HIV Behavioral Surveillance System, the HIVNET Vaccine Preparedness Study, and other published data. Annual HIV transmissions were estimated by partner type (main or casual) and by sex type (receptive anal intercourse, insertive anal intercourse, or oral sex).

Results:

Sixty-eight percent [95% confidence interval (CI) 58–78) of HIV transmissions were from main sex partners because of a higher number of sex acts with main partners, more frequent receptive roles in anal sex with main partners, and lower condom use during anal sex with main partners. By sex type, 69%(95% CI 59–79) of infections were from …