April 15, 2011
HIV-1 RNA concentrations in semen and vaginal secretions can be used as a marker for HIV transmission risk, suggests a new two-year study of serodiscordant heterosexual couples in Africa. The relation was independent of plasma HIV-1 concentrations, noted Dr. Jared Baeten, of the University of Washington-Seattle, and colleagues.
Researchers for years have known of the link between HIV concentration in the blood and the risk of transmission, Baeten said. However, no studies have been large enough to conclusively establish the same for HIV in genital secretions, beyond a working hypothesis, he said.
In the prospective study, Baeten and colleagues followed 2,521 serodiscordant heterosexual couples from seven African countries, assessing genital HIV-1 RNA quantity and transmission risk for up to two years. Couples received HIV prevention counseling, and viral sequence analysis was used to confirm subsequent HIV transmissions.
The researchers tested endocervical samples from 1,805 women, including 46 women who transmitted HIV to their partner, and semen samples from 716 men, including 32 who infected their partner.
"There was a correlation between genital and plasma HIV-1 RNA concentrations," wrote the study authors. Even so, genital HIV-1 RNA independently predicted transmission risk after adjusting for plasma HIV quantity, the study found.
"The relation was linear," Baeten said. "As the amount of HIV in the genital samples went up, the risk of transmission went up. And this was true for transmission from women to men and men to women."
Most HIV infections globally are sexually acquired, so researchers looking for a way to reduce transmission might look to genital tract HIV levels as potentially the best marker for risk, Baeten said. "Researchers can test interventions that reduce the genital HIV levels and understand that those would have a substantial effect in preventing HIV transmission risk," he said.
The study, "Genital HIV-1 RNA Predicts Risk of Heterosexual HIV-1 Transmission," was published in Science Translational Medicine (2011;3(77):77ra29).