Warning Issued Over HIV Risk from Heterosexual Intercourse

A study to be presented at the International AIDS Conference has claimed that the standard method for assessing the risk of HIV infection through heterosexual intercourse could be actually skewed.

The paper, published online late Monday by the journal The Lancet Infectious Diseases, takes issue with a yardstick widely used by epidemiologists and says it may have helped fuel misperceptions that HIV is hard to catch for heterosexuals.

This yardstick suggests that transmission of the HIV virus occurs on average once with every 1,000 acts of heterosexual intercourse between someone who is infected and another who is uninfected.

But the measurement is based on stable couples where there is a low prevalence of risk factors, according to an overview of the published evidence, led by Kimberly Powers of the University of North Carolina.

In other scenarios, these risk factors can multiply the chances of transmission by a factor of between several times and several hundred times, it suggested.

Powers' team found zero transmission after more than 100 acts of penile-vaginal intercourse among a study group of so-called serodiscordant couples -- couples in which one partner has the human immunodeficiency virus (HIV) while the other does not.

At the other end of the range, infection occurred for every 3.1 acts of heterosexual anal intercourse, the investigators found.

These risks could be amplified by other factors, such as men who were not circumcised -- circumcision has been found to provide some protection against infection -- or if a partner had genital ulcers, or was at the early or late stage of HIV infection, when virus levels are higher.