Although studies in Africa have shown that circumcision can lower the spread of HIV among heterosexuals, it may not do much to prevent infections among gay and bisexual men in Western countries, a new study suggests.

A number of studies in African nations have found that circumcised heterosexual men were up to 60 percent less likely than uncircumcised men to contract HIV during the study periods.

But it is unclear whether circumcision could have an impact on HIV transmission in the U.S. or other Western countries, where much of the transmission is among men who have sex with men. There has so far been no good evidence that circumcision lowers HIV risk among these men.

In the new study, researchers at the U.S. Centers for Disease Control and Prevention (CDC) looked at HIV infection rates among nearly 4,900 men in the U.S., Canada and the Netherlands who took part in a clinical trial of an HIV vaccine.

They found that circumcised and uncircumcised men showed no difference in the risk of HIV infection over three years.

Moreover, while having unprotected sex with an HIV-positive partner increased a man’s risk of infection, there was no evidence that circumcision altered that risk.

The findings, reported in the journal AIDS, come as the CDC is developing new recommendations on circumcision for reducing HIV transmission. The agency says it is considering whether to recommend circumcision for heterosexual men at elevated risk of HIV, and whether there is enough evidence to make any recommendations for men who have sex with men.

With regards to infant circumcision, the CDC says on its Web site, “many options are still being considered in this process, including simply recommending that health-care providers educate parents about the potential benefits and risks to ensure that parents have the information they need to make an informed decision.”

Circumcision is thought to protect men from HIV infection because foreskin tissue appears particularly susceptible to the virus, and may serve as an entry point for it.

But circumcision may not make much difference in transmission among men in Western countries for a number of reasons, according to Deborah A. Gust and her colleagues at the CDC.

One factor could be the fact that many HIV-positive people in developed countries are on powerful HIV drugs that reduce the chances of transmission, and may outweigh any effects of circumcision. In addition, Gust and her colleagues point out, circumcision would not affect HIV risk from receptive anal sex - and that, again, could outweigh any protective effect of circumcision during insertive sex.

The findings are based on data from 4,889 men who took part in an HIV vaccine trial begun in 1998; 86 percent had been circumcised. During the three-year study, 7 percent of the men became HIV-positive.

When the researchers accounted for other factors - including demographics, and HIV risk factors like drug use and having unprotected sex - circumcision showed no effect on the odds of HIV transmission.

Still, Gust and her colleagues point to some limitations of their study, including the relatively small number of uncircumcised men overall and the small number of uncircumcised men who became HIV-positive during the study - 43.

They say that future studies, with larger samples of uncircumcised men, should continue to look at the question of circumcision and HIV transmission among men who have sex with men.

The researchers also note, however, that other CDC scientists have concluded, based on their own studies, that circumcision would likely have only a “limited” impact on HIV transmission in the U.S.

SOURCE: AIDS, 2010.