In the study, published in the Feb. 15 issue of The Journal of Infectious Diseases, now available online, Jared Baeten and colleagues from the United States and Kenya collected detailed sexual data from a group of male Kenyan truckers and, using statistical models, developed infectivity measures that 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 infectivity rates calculated in the past from studies of monogamous couples. Their results may help explain the rapid spread of HIV in settings where circumcision is not common and multiple sexual partnerships are.

Between 1993 and 1997, 745 male employees of trucking companies based in Mombasa, Kenya were followed for the study. 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. At the end of the study the probability of infection was calculated using a statistical model that incorporated published data to estimate the rates of HIV infection among the three types of sexual partners.

For the men in the study, the overall probably of becoming HIV-infected following a single act of intercourse was calculated to be .0063, or one in 160. Uncircumcised men had a more than two-fold increased risk of infection per sexual act compared with circumcised men--one in 80 versus one in 200. Past studies have a
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Contact: Steve Baragona
sbaragona@idsociety.org
703-299-0412
Infectious Diseases Society of America
19-Jan-2005