Defense mechanism: circumcision averts some HIV infections.

Men who get circumcised reduce their risk of acquiring HIV, the AIDS virus, by more than half, a clinical trial in South Africa shows.

Many previous studies have suggested such a benefit from male circumcision (SN: 4/3/04, p. 212). But this trial and two ongoing trials in Uganda and Kenya are the first ones to investigate the procedure's effect on HIV risk to men. It did so by randomly assigning some men and not others to be circumcised, says physician Bertran Auvert of INSERM, the French national research agency, in Saint-Maurice.

Auvert and an international team of researchers recruited 3,274 uncircumcised heterosexual men, ages 18 to 24, from an area near Johannesburg.

All wanted to be circumcised and agreed to get the operation either at the start or at the end of the planned 21-month study. After the volunteers were randomly divided, physicians circumcised half the men and instructed them to abstain from sex for 6 weeks to allow full healing. Men in both groups were counseled on safe sex practices and checked for HIV infection three times during the study.

After 18 months, an oversight panel of scientists halted the project because the data were clear--49 of the uncircumcised men but only 20 of those who were circumcised had acquired HIV. The researchers report the findings in the November PLoS Medicine.

"There can no longer be a shadow of doubt that male circumcision gives a man major protection against HIV infection," says physiologist Roger V. Short of the University of Melbourne in Carlton, Australia, who wasn't involved in the South African study.

Auvert says that although circumcision reduced HIV risk by 60 percent, some men might mistakenly interpret this benefit as full protection. The circumcised men in the trial reported having sex 18 percent more often than the uncircumcised men did. The reason for the difference is unclear, he says.

Shortly after circumcision, men are at high risk of contracting the disease from sex partners because of the surgical wounds. But Auvert notes there was no jump in HIV infections among recently circumcised men in this study.

Uncircumcised men have soft foreskin around the head of the penis containing many cells that are easily infected by HIV, according to epidemiologist Robert C. Bailey of the University of Illinois at Chicago. These cells, called Langerhans' cells, "tend to be close to the surface," he says. Once infected, he adds, "they carry the virus deeper," to the immune system T cells that HIV most commonly infects.

Circumcision removes the foreskin. During healing after the procedure, the protein keratin toughens the skin of the penis, which reduces HIV penetration there, Bailey says.

If circumcision offers protection for young-adult men, then it would be at least as valuable--or even more so--if done earlier in life, says Bailey, who is leading the study in Kenya.

The new data support a policy of early circumcision, Short concurs. "The later in life a man is circumcised, the more likely he is to be already infected with HIV."