As clinical trials of antiretroviral treatment as prevention and pre-exposure prophylaxis (PrEP) continue to produce dramatic drops in HIV transmission, researchers are still trying to pinpoint the risk of transmission from specific sex acts.
In the May 6 online edition of AIDS, CDC researchers gave updated estimates of the risk of HIV acquisition from various types of exposure, including sexual, parenteral (for example, accidental needle-sticks or sharing injection drug equipment), and vertical (mother-to-child). They also looked at the protective effect of various prevention strategies.
Pragna Patel and colleagues did a literature search for recent studies providing new data since the last CDC estimates in 2005. They looked for articles that reported per-act risk of HIV transmission and data on modifying factors such as viral load, acute HIV infection (when viral load is highest), other sexually transmitted infections (STIs), condom use, PrEP, and use of antiretroviral therapy (ART).
After looking at some 15,000 articles, they identified 14 relevant studies of per-act risk and 15 on modifying factors. These included systematic reviews and meta-analyses that themselves included data from multiple studies.
Not surprisingly, blood transfusions posed the greatest risk, at 9,250 transmissions per 10,000 exposures. The next highest risk was mother-to-child transmission, at 2,255 per 10,000 exposures when HIV-positive pregnant women and their newborns do not receive preventive antiretrovirals—now standard practice throughout the world.
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