Circumcision appears to reduce a man's risk of contracting AIDS from heterosexual sex by half, according to U.S. government health officials.
Because circumcision was working so well that continuing clinical trials would be unethical, the officials said Wednesday that they had stopped two of the trials in Africa.
AIDS experts immediately hailed the finding, and the directors of the U.S. and international funds for fighting the disease said they would now consider paying for circumcisions.
"This is very exciting news," said Daniel Halperin, an HIV specialist at the Harvard Center for Population and Development, who has argued in scientific journals for years that circumcision slows the spread of AIDS in the parts of Africa where it is common.
In an interview from Zimbabwe, he added, "I have no doubt that as word of this gets around, millions of African men will want to get circumcised, and that will save many lives."
Uncircumcised men are thought to be more susceptible because the underside of the foreskin is rich in Langerhans cells, sentinel cells of the immune system, which attach easily to the human immunodeficiency virus, which causes AIDS. The foreskin also often suffers small tears during intercourse.
But experts also cautioned that circumcision is no cure-all. It only lessens the chances that a man will catch the virus; it is expensive compared with condoms, abstinence or other methods, and the surgery has serious risks if performed by folk healers using dirty blades, as often happens in rural Africa.
Circumcision is "not a magic bullet, but a potentially important intervention," said Kevin De Cock, director of HIV/AIDS for the World Health Organization.
Sex education messages for young men need to make it clear that "this does not mean that you have an absolute protection," said Anthony Fauci, an AIDS researcher and director of the National Institute of Allergy and Infectious Diseases. Circumcision should be used with other prevention methods, he said, and it does nothing to prevent spread by anal sex or drug injection, ways in which the virus commonly spreads in the United States, for example.
The two trials, conducted by researchers from universities in the United States, Canada, Uganda and Kenya, involved nearly 3,000 heterosexual men in Kisumu, Kenya, and nearly 5,000 in Rakai, Uganda. None were infected with HIV; they were divided into circumcised and uncircumcised groups. They were given safe-sex advice, although many presumably did not take it, and tested again regularly.
The trials started in 2001 and reached their target enrollments in September 2005. The trials were to have continued until mid-2007 but were stopped this week by the National Institutes of Health's Data and Safety and Monitoring Board. The halt came after data showed that the Kenyan men had a 53 percent reduction in new HIV infection.
Twenty-two of the 1,393 circumcised men in the study caught the disease, compared with 47 of the 1,391 uncircumcised men. In Uganda, the reduction was 48 percent. Those results echo the finding of a trial completed last year in Orange Farm, a township in South Africa, financed by the French government, which demonstrated a reduction of 60 percent among circumcised men.
The two largest agencies dedicated to fighting AIDS said they would now be willing to pay for circumcisions, which they had not before because there was too little evidence that it worked.
Richard Feachem, executive director of the Global Fund to Fight AIDS, Tuberculosis and Malaria, which has almost $5 billion in pledges, said in a television interview that if a country submitted plans to conduct safe, sterile circumcisions, "I think it's very likely that our technical panel would approve it."
Mark Dybul, executive director of the President's Emergency Plan for AIDS Relief, a $15 billion fund established by President George W. Bush, said in a statement that his agency "will support implementation of safe medical male circumcision for HIV/AIDS prevention" if world health agencies recommended it.
He also warned that it was only one new weapon in the fight, adding, "Prevention efforts must reinforce the ABC approach — abstain, be faithful, and correct and consistent use of condoms."
Researchers have long noted that parts of Africa where circumcision is common — particularly the Muslim countries of West Africa — have much lower AIDS rates, while those in southern Africa, where circumcision is rare, have the highest.
But drawing conclusions was always confounded by other regional factors, like strict Shariah law in some Muslim areas, rape and genocide in East Africa, polygamy, rites that require widows to have sex with a relative, or patronage of prostitutes by miners and migrant workers in the south.
Outside Muslim regions, circumcision is spotty. In South Africa, for example, the Xhosa people circumcise teenage boys, while Zulus do not. AIDS is common in both tribes.
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