Risk of HIV Transmission Highest in Early Stage of Infection

The risk of HIV transmission via heterosexual intercourse is highest early in the course of HIV infection, before most infected people know their HIV status, according to a new study published in the May 1 issue of The Journal of Infectious Diseases, now available online.

Conducted by a group of investigators led by Maria J. Wawer of Columbia University, the study is the first to present empirical data showing that the rate of heterosexual HIV transmission per coital act varies over the course of HIV infection. The investigators found that the risk of transmission was highest early in infection, then dropped, then rose again late in infection.

Wawer and colleagues followed a cohort of over 15,000 adults living in rural villages in Rakai, Uganda. From this population, they retrospectively identified 235 heterosexual couples in whom one partner was infected with HIV and the other partner was uninfected and monogamous. Study participants provided a blood sample and answered questions about their health and behavior, including questions on number of sexual partners and coital frequency, at 10-month intervals for up to 40 months.

From analysis of these data, the researchers found that during early infection (the approximately two-and-a-half month period after HIV seroconversion), the average rate of HIV transmission was five- to twelve-fold higher than during established infection. The infection rate was 8.2 per 1000 coital acts during early infection, compared to 0.7 to 1.5 per 1000 coital acts during established infection. The rate rose again during late-stage infection, 25 to 26 months prior to death, to 2.8 per 1000 coital acts. Among partners with newly acquired HIV infection, more than 40 percent transmitted to their partners within approximately 5 months.

These results reflect transmission rates for heterosexual vaginal intercourse only, the authors noted, and cannot be applied to HIV transmission via anal intercourse or injection drug use, since neither behavior was reported by study participants. In addition to early or late infection, other factors associated with increased transmission from the HIV-infected partner were younger age, increased viral load, and genital ulcer disease.

The study in Uganda was a collaboration between the Uganda Virus Research Institute and researchers at Makerere University, Kampala, and Columbia University and Johns Hopkins University in the United States. The study was approved by human subjects ethics boards in Uganda and the United States. All participants were offered HIV counseling and testing, health education on HIV prevention, condoms and access to STD treatment, all provided at no cost.

In an accompanying editorial, Myron S. Cohen and Christopher D. Pilcher of the University of North Carolina at Chapel Hill discussed the implications of this work for HIV prevention efforts. Traditionally, they explained, efforts have focused on those who are not yet infected and on those with established infection. The highest rate of transmission in the study, however, occurred in early infection, when few infected persons are aware of their infection status or receive the antiretroviral drugs used to treat HIV infection. Cohen and Pilcher recommended that increased attention be paid to those recently infected, and that measures such as partner notification, counseling services, and novel biological interventions be developed specifically for persons with early HIV infection.

“The challenge now,” they said, “is to waste no time finding the most creative strategies to incorporate the results of this study into global HIV prevention efforts.”