UNITED STATES: "Estimating the Proportion of HIV Transmissions from Main Sex Partners Among Men Who Have Sex with Men in Five US Cities" AIDS Vol. 23; No. 9: P. 1153-1162 (06.01.09):: Patrick S. Sullivan; Laura Salazar; Susan Buchbinder; Travis H. Sanchez

Men who have sex with men (MSM) continue to be the group most heavily impacted by the US HIV epidemic. Since 2000, HIV incidence among US MSM has been increasing.

In the current study, the researchers 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. The authors estimated annual HIV transmissions by partner type (main or casual) and by sex type (receptive anal intercourse, insertive anal intercourse or oral sex).

The data showed that 68 percent of HIV transmissions were from main partners (95 percent confidence interval (CI) 58-78). This was attributed to a higher number of sex acts with main partners, more frequent receptive roles in anal sex with main partners, and less condom use during anal sex with main partners. Sixty-nine percent of infections were from receptive anal intercourse (95 percent CI 59-79); 28 percent were from insertive anal intercourse (95 percent CI 19-38); and 2 percent were from oral sex (95 percent CI 0-5). Based on the model, the estimated HIV incidence rate was 2.2 percent (95 percent CI 1.7-2.7) per year. In sensitivity analyses, estimates of transmission from main sex partners were as low as 52 percent (95 percent CI 41-62) and as high as 74 percent (95 percent CI 68-80).

"According to our model, most HIV transmissions among MSM in five US cities are from main sex partners," the authors concluded. "HIV prevention efforts should take into account the risks of HIV transmission in male partnerships, and couples-based HIV prevention interventions for MSM should be given high priority in the US HIV prevention research portfolio."