While African trials have shown that circumcision lowers the risk of female to male HIV transmission by 60 percent, a U.S.-based study has recently found that HIV prevalence among circumcised men who have sex with men (MSM) is not significantly lower than their uncircumcised counterparts, BBC News reports.

A U.S. Centers for Disease Control and Prevention (CDC) study examined data on 53,567 MSM, of whom 52 percent were circumcised. HIV prevalence among circumcised MSM was lower, but not significantly so. This contradicts evidence collected before the introduction of antiretroviral therapy (ARV) in 1996, which showed that circumcision may be beneficial to MSM.

Experts say a few reasons could explain why circumcision is no longer effective. The perception that HIV is now a manageable illness may increase risk-taking behavior among MSM, thus canceling out any benefits of circumcision. In addition, recent studies show that those on HAART are less likely to transmit the virus to their partners; therefore, the drugs may lower the risk of transmission to the point where circumcision is no longer a factor. BBC News reports that a third possibility: The pre-ARV studies may have enrolled a smaller percentage of MSM who primarily engaged in receptive anal sex, which carries the greatest HIV infection risk among this group.