Viral loads of people infected with HIV differ based on gender, suggests new research that may have implications for treatment. During the first few years of infection, women have significantly smaller amounts of the HIV virus in their blood than men. Surprisingly, however, they lose immune cells and develop AIDS just as quickly, according to a new study by the National Institute of Allergy and Infectious Diseases (NIAID), published in todays New England Journal of Medicine.

From 1988 to 1998 the researchers observed 156 men and 46 women who were HIV-positive. Of the 202 participants, 44 developed AIDS29 of them men, 15 women. The team found that the median initial viral load of women was almost five times lower than that of men as they progressed to AIDS. "Despite early differences in viral load among men and women, as time went on, both men and women had a similar risk of developing AIDS," says Timothy Sterling, assistant professor of medicine and epidemiology at Johns Hopkins University, which participated in the study.

Viral load normally determines when a person becomes eligible to start anti-HIV drug treatment, but the new findings show that this measure may be inadequate. "Previous studies in men have shown that initial viral load can be used to gauge their likelihood of progression to AIDS," says Thomas Quinn, a senior investigator for NIAID and professor at Johns Hopkins. "But these data confirm that the initial viral load is much lower in women than in men and consequently not as predictive for women." Although this sheds a light on gender differences in viral loads, Quinn adds that the best point at which to start anti-HIV drug treatments is generally still unknown.