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Male Circumcision Reduces Risk of HIV Transmission From
Women to Men20 Jan 2005
The
first study to examine the probability of HIV infection per
act of heterosexual sex among a population with multiple
sexual partners has found that uncircumcised men have more
than twice the risk of acquiring HIV than do circumcised men.
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 also found greater HIV infection
risk for uncircumcised men. Unlike those studies, however, the
present study was also able to take into account cultural
characteristics that might be responsible for differences in
sexual behavior. These differences could, in turn, 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.
In addition to the results on
circumcision, 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 cohorts 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. Taken with the authors' evidence that
female-to-male infection rates may be more than two-fold
greater for uncircumcised men, this new information may help
us understand why the virus is spreading rapidly in parts of
Africa, and help define better HIV strategies for prevention
in these settings.
Founded in 1904, The Journal of
Infectious Diseases is the premier publication in the Western
Hemisphere for original research on the pathogenesis,
diagnosis, and treatment of infectious diseases; on the
microbes that cause them; and on disorders of host immune
mechanisms. Articles in JID include research results from
microbiology, immunology, epidemiology, and related
disciplines. JID is published under the auspices of the
Infectious Diseases Society of America (IDSA). Based in
Alexandria, Va., IDSA is a professional society representing
more than 8,000 physicians and scientists who specialize in
infectious diseases. Nested within the IDSA, the HIV Medicine
Association (HIVMA) is the professional home for more than
2,700 physicians, scientists and other health care
professionals dedicated to the field of HIV/AIDS. HIVMA
promotes quality in HIV care and advocates policies that
ensure a comprehensive and humane response to the AIDS
pandemic informed by science and social justice. For more
information, visit the Infectious Diseases Society of
America.
Steve
Baragona
sbaragona@idsociety.org
Infectious
Diseases Society of America
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