Black men who have sex with men (MSM) are seven times more likely than their white counterparts to be infected with HIV. The reason for this is unclear, in light of new research presented yesterday at the 2007 National HIV Prevention Conference in Atlanta suggesting that they are no more likely to engage in high-risk sex and are actually less likely to use street drugs than white MSM.

To verify and possibly explain this observation, Gregorio Millett, MPH, of the U.S. Centers for Disease Control and Prevention in Atlanta and his colleagues combined and reviewed the results of other studies published between 1974 and 2006 finding a discrepancy between risk taking and HIV incidence in black MSM. Fifty-three studies, including more than 60,000 MSM, were included in the analysis.

Taken as a whole, the studies found that black MSM were no more likely than white MSM to have reported unprotected anal intercourse 12, 6 or 3 months—or during their most recent encounter encounter—prior to being surveyed. Similarly, black MSM were no more likely than white MSM to report using soft recreational drugs like marijuana, poppers or hallucinogens, or harder drugs like amphetamines, injection drugs, crack cocaine or opiates. In fact, when the researchers controlled for age, they found that young black MSM were less likely than their white counterparts to report drug use. This finding is significant, given that other studies have found a strong association between drug use and HIV infection rates.

When Millett’s team used two methods to analyze the studies by publication date, differences were noted. In the first method, they divided the studies into three categories: the early epidemic (between 1980 and 1990), the middle epidemic (1991 to 2000) and the recent epidemic (2001to 2006). In the second method they separated the studies into two categories: before the availability of highly active antiretroviral therapy (HAART) and after HAART. They found that in the early epidemic black MSM did report higher rates of unprotected anal intercourse than white MSM. The difference disappeared by 1991. The team also found higher rates of unprotected anal intercourse among black MSM during the pre-HAART era, but not in the more recent years of HAART.

The fact that the epidemic gained an early foothold in the black MSM community, Millet explained during his presentation, may account for the disparity in HIV prevalence between black and white MSM. Since many black MSM have sex only with other black MSM—and because the prevalence of HIV is higher in the black MSM community—they are more likely to be exposed to the virus than white men who have sex only with other white men.

In a recent study, Millet added, 64 percent of black MSM who tested positive hadn’t known or suspected their HIV status, and that several studies have found that black MSM are less likely to be on HAART than white MSM. This, Millett reasoned, suggests that black MSM partners are more likely to have high viral loads—and thus be more infectious—than white MSM partners, further compounding the chance that black MSM will become infected despite taking no greater risks than their white counterparts.