Every Saturday the CSPH highlights news or recent research in the field of human sexuality. This week we’re discussing recent research published in The Journal of Infectious Diseases, a publication from The Infectious Diseases Society of America, which states the level of the HIV-1 virus in the blood of an HIV-infected person is the single most important risk factor for sexual transmission of HIV to an uninfected partner.
The finding is based on a study of 3,300 heterosexual, HIV-discordant couples (one partner has HIV and the other is HIV-free) in sub-Saharan Africa. The researchers were able to calculate the risk of HIV-1 transmission per act of sexual intercourse and found the average rate of infection to be about one per 900 acts of sexual intercourse and the level of HIV-1 RNA in the blood of the infected partner was the most important factor in HIV transmission. The higher the viral load in the infected partner, they found, the higher the risk of transmission. The study also confirmed that condoms are highly protective, reducing the risk of HIV transmission by 78 percent when subjects reported using a condom. Older age was also associated with reduced transmission per sex act supporting the possibility of a significant decline in the infectivity of HIV with age. Male circumcision reduced female-to-male transmission by approximately 47 percent supporting data released by the Centers for Disease Control that the foreskin is more susceptible to HIV infection than other penile tissue because of its higher density of target cells for infection and greater susceptibility to tearing during intercourse. Genital herpes infections and the presence of genital ulcers were associated with increased rates of transmission for the same reason because of the increased points of entry for pathogens in open sores and areas of infection.
“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 researchers stated. The researchers also plan to use the genetic data collected from this study along with new data from another recently completed clinical trial to explain the variation in transmission risk among couples.
The strengths of this study include the large number of couples, molecular confirmation of HIV transmission between partners, repeated RNA measurements over follow-up, and relatively short intervals of 3 months between tests. The Infectious Diseases Society of America claims that previous studies examining risk factors for sexual transmission of HIV have been significantly smaller and not as comprehensive. Ronald H. Gray, MD, and Maria J. Wawer, MD of Johns Hopkins University in Baltimore (not involved in the study), claimed after reviewing this research that it is “possibly the most precise estimates of HIV-1 transmission per sexual act during latent HIV disease, providing a valuable addition to knowledge in this area, where much remains to be learned.”
This study makes an important statement about how certain HIV positive individuals are more contagious than others depending on their viral load at the time of sexual intercourse. One huge limitation to this study is that only heterosexual vaginal intercourse was used to measure transmission. While this study does gives hope that more effective treatments for preventing the transition from HIV to AIDS can be created and it is important for the public to learn more about the disease, it is extremely important for HIV positive individuals to be educated about the risks of transmission at any stage and for their sexual partners to be informed of the risks for infection. More studies about levels of transmission risk should be done to include non-heterosexual activity and more than just vaginal intercourse.