Researchers Find Vaginal Bacteria Imbalance Might Boost AIDS Risk

CHAPEL HILL - In 1997, University of North Carolina at Chapel Hill scientists showed that sexually transmitted diseases increase susceptibility to HIV -- the virus that causes AIDS. They also demonstrated that people infected simultaneously with HIV and other sexually transmitted diseases shed more of the deadly virus in their genital secretions than doctors expected and that treating men for urethral infections reduced HIV in semen.

Now, the public health and medical school researchers have identified a link in pregnant women between HIV infections and changes in bacteria normally found in the vagina.

A study of 724 pregnant N.C. women found that four times as many subjects with an imbalance in naturally occurring vaginal bacteria were HIV-infected as those with a normal bacterial balance. Doctors call the condition, in which percentages of various bacteria shift radically, bacterial vaginosis.

"We cannot determine at this point whether vaginal bacteria abnormalities increase women's susceptibility to HIV infection or become more common after infection with that virus," said Dr. Rachel Royce, assistant professor of epidemiology. "Studies that have come out about work in Africa since our paper was accepted, however, suggest that women with bacterial vaginosis, or BV, are more susceptible to HIV infection."

A report on the study -- the first of its kind in developed countries, where AIDS is far less common than in Africa and Southeast Asia -- appears in the April issue of the Journal of Acquired Immune Deficiency Syndromes and Human Retrovirology. Besides Royce, authors are Drs. John Thorp, associate professor of obstetrics and gynecology; Juan L. Granados, a UNC-CH faculty member on the Wake Medical Center staff; and David A. Savitz, professor and chair of epidemiology.

"These findings may explain why black women have been disproportionately affected by HIV, something we have not understood before," Royce said. "This work also shows is that it's very important for us to find out more about changes in vaginal ecology and bacterial vaginosis. We might need to treat BV more aggressively than we did in the past."

The normal balance of microorganisms may protect against infections through secretion of acidic chemicals, she said. When women's genital tracts become more alkaline, HIV apparently can survive in greater amounts.

Last month, Royce and her colleagues reported in a study of 819 pregnant N.C. women that overall, 15 percent of subjects showed BV. What was especially interesting, she said, was that the condition appeared in 22 percent of blacks, but in only 9 percent of whites.

"We don't understand yet why there was this difference, but it's important because it also may partially explain why black women are more likely than whites to deliver their babies pre-term," Royce said. "We have never known why that is. We do know, however, that when women are treated aggressively for BV, pre-term delivery decreases significantly."

Racial differences in vaginosis remained in both studies even after scientists controlled for social and demographic factors, sexual activity, hygiene, health behaviors and infection with sexually transmitted diseases.

Researchers overall found a significant decline in the Lactobacillus-dominated flora normally present in the vagina and a strong increase in such anaerobic bacteria as Gardnerella vaginalis and Mobiluncus, which was 10 times more common in blacks than in whites.

A paper describing the earlier work appeared in the February issue of the journal Sexually Transmitted Diseases.

Note: Royce is in Southeast Asia until April 5, but then can be reached at 919-966-7440. Thorp's number is 966-1601.