By DANIEL Q. HANEY, AP Medical Editor
CHICAGO (AP) - A study of heterosexual couples in Africa
concludes that the chance of catching the AIDS (news - web sites) virus from a single
sexual encounter with an infected person is one in 588.
This risk is calculated for people who do not use condoms and
who have sex regularly with one infected partner.
Earlier estimates from North America and Europe vary but have
generally placed the risk at about one in 1,000 for heterosexuals.
In this study, researchers followed 174 sexually monogamous
couples in Rakai, Uganda, in which one partner had HIV (news - web sites) and the
other did not. They were given condoms but usually did not use
them. Typically the couples had sex nine or 10 times a month, and
over time, 38 people became infected.
Earlier data from the same research team showed that the risk of
people transmitting HIV is slight if the amount of virus in their
bloodstream is low. Those findings have encouraged the belief that
the wide use of AIDS drug combinations, which make virus levels
fall dramatically, will slow the spread of the disease.
The latest figures were presented by Dr. Ronald H. Gray of Johns
Hopkins University at the Eighth Annual Retrovirus Conference in
Chicago, which concluded Thursday.
Among the findings:
-Infected teen-agers are three times more likely than people
over 40 to spread HIV to others during each sexual encounter. This
difference cannot be explained by the fact that young people are
more sexually active.
-The risk that an HIV-infected woman will transmit the virus to
an uninfected man is one in 454. For an infected man to an
uninfected woman, it is one in 769. This difference is not large
enough to be statistically meaningful, and many have assumed that
HIV spreads more readily from men to women than vice versa.
-The risk of spread depends greatly on how much virus people
carry. In those whose level of virus is less than 1,700 copies per
milliliter of blood, the risk is one in 10,000. When levels are
over 38,500, risk is one in 294.
-The risk of transmission appears to be the same for different
subtypes of virus. Some have speculated that AIDS is much more
prevalent in Africa because a different variety of the virus
-None of the circumcised men in the study caught HIV. Some
experts have raised the possibility of promoting circumcision as a
way to control the epidemic.
Whether the transmission risk is the same among couples outside
Africa is unclear, especially since virus levels may be higher in
Africa, where so few infected people get treated. However, Dr.
Helene Gayle, AIDS chief at the U.S. Centers for Disease Control
and Prevention (news - web sites), said the latest data at least offer a general
estimate of this risk.