Amid news that the U.S. Centers for Disease Control nd Prevention (CDC) will likely soon release higher figures for estimated annual HIV infections, several recent studies have looked at HIV transmission and prevention among men who have sex with men (MSM), who continue to bear the brunt of the epidemic in the U.S.

Studies have shown that black MSM are about twice as likely as white MSM to be HIV positive, and may be as much as 7 times more likely to become newly infected. According to an analysis presented at the conference, young black MSM have experienced the largest recent increase in new HIV diagnoses.

Based on data from the U.S. National HIV/AIDS Reporting System, Joseph Prejean from the CDC and colleagues (abstract B08-5) found that black MSM born in the 1965-1969 period had a high but stable rate of new HIV infections between 2001 and 2005, while those born in 1975-1979 or 1980-1984 experienced a rising rate. (Importantly, this analysis is based on data from the 33 states with long-term names-based HIV reporting, which excludes some areas with the highest estimated HIV rates.)

However, the reasons for the higher HIV incidence rate among black MSM are unclear, since they do not appear more likely to engage in high-risk behavior. 

Gregorio Millett and colleagues from the CDC (abstract A03-1) conducted a systematic review of 53 studies published between 1980 and 2006, which included a total of more than 60,000 MSM.

However, breaking down the data by time period showed that black MSM did have higher rates than whites of high-risk sexual behavior in the early years of the epidemic (1980-1990), although this difference was no longer present by the middle (1991-2000) and late (2001-2006) periods.

Millett suggested that the difference in risk behavior early in the epidemic allowed more black MSM to become infected, and the group continues to have a higher rate of new infections since many MSM tend to have sex and use drugs primarily with people of the same race/ethnicity.

In other words, a black man who only has sex with other black men faces a higher likelihood of encountering HIV positive partners than a white man who only has sex with other white men, and thus is at greater risk of infection even if he engage in exactly the same activities.

Millet also suggested -- based on recent evidence indicating that black MSM may be less likely than white MSM to know their HIV status or to be taking antiretroviral therapy -- that black HIV positive men may be more likely to have a higher viral load, which facilitates HIV transmission. Further, black MSM have higher rates of other sexually transmitted diseases (such as syphilis), which can increase the risk of both transmitting and contracting HIV.

Circumcision in the U.S.

Serosorting

The researchers aimed to assess whether MSM who practice serosorting differ with regard to their risk for HIV transmission compared with non-serosorters. They administered surveys to 628 self-identified HIV negative MSM at gay pride events in June 2006 (an impressive 80% response rate).

About one-third of the survey respondents (229 men) reported that they engaged in serosorting. Men who practiced serosorting were more likely to believe that it offered protection against HIV transmission, perceived themselves to be at no relatively higher risk for HIV transmission, and had unprotected anal intercourse with more partners. More than half the men said they received HIV tests once yearly or less, and the testing frequency was similar for serosorters and non-serosorters.

“Men who identify as HIV negative and serosort are no more likely to know their HIV status than men who do not serosort and are at higher risk for exposure to HIV,” the investigators concluded. “Interventions targeting MSM must address the limitations of serosorting.”