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AIDS: Heterosexual Infectivity Rates Vary by HIV Risk Factors

Anal intercourse, circumcision status, genital ulcer disease can dramatically increase rates

TUESDAY, Aug. 5 (HealthDay News) -- Among heterosexual couples in which one partner is HIV positive, the commonly accepted infectivity rate of one transmission per 1,000 sexual contacts does not take into account risk factors that can increase the rate by up to several hundred times, according to a review published online Aug. 5 in The Lancet Infectious Diseases and presented at AIDS 2008, the International AIDS Conference held Aug. 3 to 8 in Mexico City.

Kimberly A. Powers, of the University of North Carolina in Chapel Hill, and colleagues conducted a systematic search through April 27, 2008 to identify articles estimating the heterosexual infectivity of HIV-1.

The researchers found that that infectivity rates varied from zero transmissions after more than 100 penile-vaginal contacts to one transmission for every 3.1 episodes of heterosexual anal intercourse. They also found that infectivity rates per 1,000 contacts were higher among uncircumcised susceptible men compared to circumcised susceptible men (13.2 versus 5.1) and among subjects with genital ulcer disease (7.5 versus 1.5).

"Future infectivity studies should carefully count infectious exposures and rigorously account for transmission cofactors. Improved infectivity estimates -- especially more detailed estimates that quantify the amplifying effects of biological cofactors -- will help us to grasp the magnitude of the HIV epidemic, accurately communicate the level of risk involved in heterosexual sex, and identify the best possible intervention strategies for slowing the epidemic's spread," the authors conclude.

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