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 inj
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Contact: Steve Baragona
sbaragona@idsociety.org
703-299-0412
Infectious Diseases Society of America
6-Apr-2005