Africans Transmit HIV at a Higher Rate

According to a new study conducted in Africa, a heterosexual person infected with HIV will transmit the virus to their partner once in every 900 times the couple has unprotected sex. The amount of virus in the blood is the single most important factor in determining whether HIV is passed between sexual partners, the study found. For every tenfold increase in the concentration, there is about a threefold increase in the risk of transmission during a single sexual act. People with very high blood concentrations of the virus (such as those who very recently acquired the infection) may need to have sex only 10 times to transmit the virus, Hughes said. The best methods for reducing HIV transmission are those that decrease the concentration of the virus in the blood, as can be done with antiretroviral drugs, Hughes said. A study published last year found the drugs could reduce the transmission of HIV between partners by 96 percent. The new study also confirmed condoms are highly effective in preventing HIV infection, reducing the risk of transmission by 78 percent. Male circumcision reduced the risk of HIV transmission by 47 percent. The new study included 3,297 couples from sub-Saharan Africa that were "HIV-discordant," meaning one partner had HIV while the other did not. The HIV-infected partners in the study were tested periodically over the two-year study for the amount of HIV in their blood. Infected partners were also interviewed every month and asked how many times they had sex, and whether they used protection. The uninfected partners were tested periodically to see whether they had acquired HIV. The researchers used genetic testing of the virus to confirm that any new HIV infections had been acquired from the study partner designated at the study's start. Eighty-six HIV transmissions occurred during the study period. Men were about twice as likely to transmit HIV to women as women were to men. This increased risk of transmission could be attributed to higher virus concentrations in the blood of men compared with women, according to the study. In addition, women were more likely to have genital herpes, which increases susceptibility to HIV. The number of sexual acts needed to transmit the virus is likely specific to the African population studied, Hughes said. Previous studies in the United States have found a lower transmission rate.