Heterosexual African-American men who have been circumcised are less likely than non-circumcised men to become infected after being exposed to HIV, according to a U.S. study published in the January 1 issue of the Journal of Infectious Diseases and reported by ScienceDaily.

In the past two years, three very large African studies have found that being circumcised significantly protects heterosexual men from becoming infected with HIV. The reduction in HIV transmission has been as high as 60 percent. Scientists have shown that the cells of the foreskin, which is removed during circumcision, are more vulnerable to HIV infection, and thus explain the increased risk in uncircumcised men. Several smaller studies have hinted the same may be true in the United States. The small number of uncircumcised American men, combined with a relatively low HIV prevalence rate among most heterosexuals, however, has made it difficult to definitively show the degree to which circumcision may protect U.S. men from infection.

To determine the impact of circumcision in heterosexual men in the United States, Lee Warner, PhD, MPH, from the Centers for Disease Control and Prevention (CDC) in Atlanta, and his colleagues studied the medical records of 26,448 African-American men in Baltimore. The men all stated that they had sex only with women and that they did not inject drugs. Most—86 percent—were circumcised.

Warner’s team found that circumcision reduced the rate of HIV transmission by 50 percent among men who’d had unprotected sex with a woman known to be HIV positive. Among the uncircumcised, 22 percent of those potentially exposed to HIV eventually tested positive for the virus, compared with 10.2 percent of the HIV-exposed circumcised men.

As for men who’d had unprotected sex with women whose HIV status they did not know, circumcision was not significantly associated with a reduction in HIV transmission. The overall rate of HIV transmission among this group was quite low, however—less than 3 percent—making it more difficult to show a difference.

In an accompanying editorial, Ronald Gray, MBBS, MSc, noted the results of this study may be particularly vital for African-American and Hispanic men, who are less likely to be circumcised and have higher rates of HIV infection. He says that the American Academy of Pediatrics does not currently recommend circumcision for babies and that Medicaid doesn’t cover the cost. “It is to be hoped,” Gray wrote, “that [this study], in conjunction with the weight of evidence from international studies, will persuade the academy to recognize the public health importance of this surgery for prevention of HIV in minority U.S. populations.”