HIV Risk From Heterosexual Intercourse May Be Underestimated

The standard method for assessing the risk of HIV infection among heterosexuals could be underestimating the potential for transmission, according to a new overview of published evidence. The study was presented at the 17th International AIDS Conference in Mexico City.

Currently, epidemiologists widely believe that HIV transmission occurs on average once every 1,000 acts of heterosexual intercourse between serodiscordant couples.

However, according to Kimberly Powers of the University of North Carolina, who led the research, this estimate is based on stable couples who have a low prevalence of risk factors. In other situations, increased risk factors can multiply the chance of transmission greatly.

Powers' team found zero transmission after more than 100 acts of penile-vaginal intercourse among a group of heterosexual serodiscordant couples. On the other hand, infection occurred for every 3.1 acts of heterosexual anal intercourse. Other risk factors could further increase transmission, such as men not being circumcised, genital ulcers, or late-stage HIV infection, when viral loads are higher.

"The use of a single, one-size-fits-all value for the heterosexual infectivity of HIV-1 obscures important differences associated with transmission cofactors," the study said. The measurement of one infection per 1,000 acts of intercourse "seems to represent a lower bound. As such, this value substantially underestimates the infectivity of HIV-1 in many heterosexual contexts."

The study adds that much remains to be discovered regarding heterosexual infectivity, such as the risk of oral sex.

The study, "Rethinking the Heterosexual Infectivity of HIV-1: A Systematic Review and Meta-analysis," was published in the Lancet Journal of Infectious Diseases (2008; doi: 10.1016/S1473-3099(08)70156-7).

Back to other news for August 2008