1 in 900. Those are the odds of contracting HIV through heterosexual sex from an infected partner, a new study has found.
The study, published in the Journal of Infectious Diseases, calculated the risk of HIV transmission per act of sexual intercourse by tracking 3,397 couples in Sub-Saharan Africa -- where one person was HIV-positive and the other was not.
Researchers concluded the average rate of infection to be about 1 per 900 acts, but noted that number can vary depending on the amount of the virus in the infected person's blood.
The findings, by researchers from the University of Washington in Seattle and elsewhere, also confirmed that condoms are highly protective -- reducing HIV infectivity by 78 percent. In addition, the “viral load” – the level of HIV in the blood of an infected partner -- is the single most important factor influencing risk of sexual transmission to an uninfected partner. As a result, lowering the viral load in HIV-infected patients can also reduce the risk of transmission.
Other factors that reduced HIV risk, the study found:
* Older couples were less likely to become infected.
* Men infected with HIV were twice as likely to transmit the AIDS virus to uninfected women as women to men.
* Male circumcision reduced female-to-male transmission by approximately 47 percent.
* Genital herpes infections and genital ulcers were associated with increased rates of transmission.
"Our results underscore the importance of antiretroviral therapy, and, possibly, treatment of co-infections, to reduce plasma HIV-1 viral load in HIV-1 infected partners, and condom promotion, male circumcision, and treatment of symptomatic sexually-transmitted infections for HIV-1 uninfected partners as potential interventions to reduce HIV-1 transmission," the authors wrote.