Circumcising adult males in two African countries reduced their risk of contracting HIV by half, according to studies that could prompt calls for programs to encourage circumcision.
Evidence from the clinical trials in Uganda and Kenya was so overwhelming that the National Institutes of Health closed them so researchers could offer the procedure to all participants.
"This was pretty much of an unequivocal type of decision based on the data," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease, said at a news briefing yesterday. "This is not iffy data."
Scientists heading the trials enrolled previously uncircumcised men who tested negative for the AIDS virus. Then, doctors circumcised half the men, and tracked infection rates among those who received the surgery and those who did not. Almost 8,000 men were enrolled across the two trials.
Three years into the trials, newly circumcised men in Uganda had a 53 percent lower infection rate than those who weren't circumcised. In Kenya, infections were 48 percent lower among circumcised volunteers.
With 2.8 million new infections occurring annually in sub-Saharan Africa, circumcision now looms as a potentially powerful tool to curb an epidemic that has left millions of children orphaned and has crippled the economies of many nations.
"There is an overwhelming body of evidence now to suggest that men who are circumcised are at approximately half the risk of HIV compared to men who are not circumcised," said Dr. Ronald Gray, lead investigator of the Uganda study and a professor at Johns Hopkins Bloomberg School of Public Health.
Researchers tracked infections acquired only through heterosexual intercourse. Though they did not have sufficient time to study the impact on women, Fauci said male circumcision could also lead to fewer infections among female partners.
The World Health Organization plans to hold a meeting early next year to consider how data from the new studies should be converted into action. The conference will be attended by many of the leading international agencies fighting the epidemic.
Not a substitute
Programs to circumcise adult men could avert millions of new infections in the region, said Fauci, while emphasizing that the procedure is not a substitute for risk-reducing precautions. These include using condoms and limiting the number of sexual contacts.
Circumcision, performed on about 60 percent of newborn boys in the United States but fewer in other regions of the world, is a procedure in which the foreskin covering the penis is removed. Though it is commonly done for religious reasons - it is dictated by Jewish and Muslim texts - some doctors theorize that it provides biological protection against HIV infection.
One theory, according to Gray, is that the inner surface of the foreskin is rich in the type of immune cells targeted by HIV. The tissue also lacks keratin, a tough protein that normally coats the skin.
"The second thing is that the foreskin is liable to tear during intercourse," Gray said, explaining that such tears give entry points for infection.
The notion that circumcision can protect a man from HIV goes back to the 1980s, when a study in Nairobi, Kenya, showed an association between circumcision and lower infection rates. "The evidence has been accumulating ever since," Gray said, noting that approximately 40 studies have suggested a benefit.
But a study in South Africa was the first to divide volunteers into two groups - circumcised and uncircumcised men - and track their infections over time. Results of that study, published in 2005, showed a 60 percent reduction in HIV infection among circumcised men.
Because circumcision is a surgical procedure that carries a potential risk of bleeding and infection, public health officials weren't ready to make public health recommendations based on one study.
Now, with two additional studies showing similar benefits and no serious risks, it appears likely that international health authorities will recommend programs to promote circumcision at least in sub-Saharan Africa.
Even so, experts noted that international assistance will be needed to help train doctors, provide clean surgical facilities and pay for circumcisions, which cost about $60 per patient. Dr. Kevin De Cock, director of the HIV/AIDS Department of the World Health Organization, also said that programs cannot be started without "country ownership."
"If decisions are made to scale this up by different countries," he said, "it does have the potential to prevent many tens of thousands, many hundreds of thousands, and perhaps millions of infections over the coming years."
Circumcision varies widely throughout Africa. Due to religious dictates, most newborns in the largely Muslim nations of northern and western Africa are circumcised. The practice is far less common in sub-Saharan Africa, where only some religious groups promote it.