Circumcising men who have sex with men (MSM) is likely to have a negligible effect on the rate of new HIV cases in the United States, according to a survey conducted in San Francisco in 2008 and reported Thursday, July 22, at the International AIDS Conference in Vienna.

Clinical trials in South Africa, Uganda and Kenya have indicated that heterosexual men who undergo circumcision are 60 percent less likely to become infected compared with uncircumcised men. Ever since these findings, public health leaders have sought to promote circumcision as a proven, cost-effective method. In Vienna, ambassador Eric Goosby, the U.S. global AIDS coordinator, and David Okello of the World Health Organization, along with Bill Clinton and Bill Gates, lent their voices to support male circumcision in Africa.

Circumcision is thought to reduce the risk of HIV transmission by removing cells in the foreskin that are most susceptible to infection by the virus.

Whether or not circumcision of adult males in the United States, notably men who have sex with men, will influence the incidence of HIV in this country remains a matter of debate. As recently as March, an analysis of data collected in the United States and other Western countries indicated that circumcision will not necessarily prevent transmission among MSM.

To explore this further, Jonathan Fuchs, MD, MPH, of the San Francisco Department of Health and his colleagues conducted a survey of MSM in San Francisco measuring HIV prevalence, circumcision status, condom use with insertive and receptive anal intercourse, and willingness to be circumcised.

Of the 521 MSM surveyed, 115 (21.1 percent) were HIV positive and 327 (62.7 percent) were already circumcised, leaving 69 (13.2 percent) for whom circumcision may have an additional preventive benefit.

Among those for whom circumcision may confer a protective effect—those who predominantly engaged in insertive anal intercourse (21.7 percent reported “topping” at least 80 percent of the time, without condoms, with their five most recent partners)—only three (0.5 percent) were willing to participate in an MSM circumcision trial. What’s more, only four (0.7 percent) were willing to get circumcised, even if it proved to be a safe method that did reduce the risk of HIV transmission.

Extrapolating these findings to the entire MSM population of San Francisco—an estimated 65,700 people, Fuchs indicated—only 500 men would potentially benefit from circumcision.

Fuchs and his team concluded that circumcision as an HIV prevention strategy would apply to few MSM in San Francisco and thus, even if effective, would have limited influence on HIV incidence in this population. However, if shown to be an effective prevention strategy for MSM, the researchers argue, circumcision could potentially benefit MSM populations with low rates of circumcision and condom use among those who engage in predominately insertive anal intercourse.