This can help researchers better understand "the natural protections that the penis, the vagina and the rectum have that we want to make sure we preserve," he said. The study "is highlighting what we need to look at going forward," he added.
Still, the study, which Anton said was "really well done," has some limitations. It only looked at heterosexual couples and not at people at higher risk of becoming infected with HIV, such as sex-trade workers and gay men.
And the study doesn't examine how often HIV-positive people with no detectable virus in their blood transmit the disease to their partners. Anti-HIV drugs can often reduce the level of HIV in blood to zero, while the virus hides in other parts of the body.
Worldwide, more than 7,000 new HIV infections are diagnosed daily, according to background information in Anton's commentary. In the big picture, these new findings can only do so much to curb the rate of HIV infection, he said.
Noting that many HIV-positive people are unaware they have the disease, Anton said, "The biggest issue in transmission is that many people don't know their status."
For more about HIV/AIDS, visit the U.S. National Library of Medicine.
SOURCES: Jared M. Baeten, M.D., Ph.D., University of Washington, Seattle; Peter A. Anton, M.D., professor of medicine and director, University of California Los Angeles, Center for Prevention Research, David Geffen School of Medicine, Los Angeles; April 6, 2011, Science Translational Medicine
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