More Evidence That Circumcision Reduces Risk of HIV

24 January 2005
More Evidence That Circumcision Reduces Risk of HIV
by George Atkinson

In a study published in the The Journal of Infectious Diseases, Jared Baeten and co-researchers from the United States and Kenya collected detailed sexual data from a group of male Kenyan truckers and used statistics to estimate the per-sexual-act probability of HIV transmission. The study is the first to calculate the probability of infection for men who have multiple, concurrent heterosexual partners, which was found to be significantly higher than infection rates from studies of monogamous couples. The results may help explain the rapid spread of HIV where circumcision is not common and multiple sexual partnerships are.

The study was carried out between 1993 and 1997 with male employees of trucking companies based in Mombasa, Kenya. Initially they were evaluated for circumcision status and HIV-negativity. Over the length of the study the men were asked to give information concerning the number of sexual encounters with three different partner types - wives, casual partners, and prostitutes - and were screened for HIV and other sexually transmitted infections. For the men in the study, the overall probability of becoming HIV-infected following a single act of intercourse was calculated to be 1 in 160. Uncircumcised men had a more than two-fold increased risk of infection per sexual act compared with circumcised men 1 in 80 compared to 1 in 200.

Earlier studies also found greater HIV infection risk for uncircumcised men. Unlike those studies, however, the present study was able to take into account cultural characteristics that might be responsible for differences in sexual behavior. These cultural characteristics could account for differences in the risk of infection. But the researchers found that cultural differences in sexual behavior did not matter; when groups of men were excluded from the analysis based on ethnic or religious characteristics, the difference in probability of infection related to circumcision status did not change.

Another significant result of the study was the high overall rate of per-contact infection. In past studies that attempted to calculate the probability of female-to-male infection through heterosexual sex, the subjects consisted only of monogamous couples in which the female partners were HIV-positive. However, in some areas of Africa where HIV infection rates are highest, multiple, concurrent partnerships are more common than monogamous couplings. Past studies of monogamous couples found that the probability of HIV transmission per-act of sexual intercourse was on the order of one in 1000 or less, much lower than the probability of one in 160 found in this study. These findings may help explain why the virus is spreading rapidly in parts of Africa.

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