By Robert Bazell Chief science and health correspondent
NBC News
updated 12/29/2006 1:40:44 PM ET 2006-12-29T18:40:44

Circumcising adult men is an effective way to limit transmission of the virus that causes AIDS. The National Institutes of Health announced today that two clinical trials in Africa have been stopped because an independent monitoring board determined the treatment was so effective that it would be unethical to continue the experiment.

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"We now have confirmation — from large, carefully controlled, randomized clinical trials —showing definitively that medically performed circumcision can significantly lower the risk of adult males contracting HIV through heterosexual intercourse," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease. "While the initial benefit will be fewer HIV infections in men, ultimately adult male circumcision could lead to fewer infections in women in those areas of the world where HIV is spread primarily through heterosexual intercourse."

The NIH has been sponsoring two trials — one with 5,000 men, ages 15 to 49, in Uganda and  a second with 2,784 men, 18-24, in Kenya. Half the men voluntarily underwent circumcision. The men were then monitored for about two years. Far more of the uncircumcised men became infected with HIV.

The studies found that the circumcised men in the Kenyan study were 48 percent less likely to get infected and 53 percent less likely in the Ugandan study.

This finding appears to apply only to heterosexual transmission, which is the main mode of  spread in Africa.

Male circumcision is common at birth in the United States. But in sub-Saharan Africa, home to more than half of the world’s almost 40 million HIV-infected people, there are large swaths of populations where male circumcision is rare.

Circumcision is not perfect protection, Fauci stressed. Men who become circumcised must not quit using condoms nor take other risks — and circumcision offers no protection from HIV acquired through anal sex or injection drug use, he noted.

“It’s not a magic bullet, but a potentially important intervention,” agreed Dr. Kevin De Cock of the World Health Organization.

These findings present enormous ethical and policy decisions which have yet to be addressed.  But scientists say the reduction of infection is so substantial that the findings cannot be ignored.

The Associated Press contributed to this report.

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