NEW YORK (Reuters Health) - A pregnant woman's risk of bacterial vaginosis, the most common type of vaginal infection and a risk factor for preterm birth, is doubled if she or her male partner is black. Those findings were presented earlier this week at the 34th annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology in Boston.

Bacterial vaginosis, which is not sexually transmitted, occurs when there is an overgrowth of certain bacteria in the vagina. A foul-smelling discharge is a common symptom. The disease can be effectively treated with various antibiotics and creams.

"In the U.S., there is a large racial disparity in terms of preterm birth; it's twice as common among black women as white women," Dr. Hyagriv Simhan told Reuters Health. "An important risk factor for preterm birth is bacterial vaginosis, for which there is also a racial disparity," he added.

Simhan and colleagues at the University of Pittsburgh School of Medicine, studied 325 women in their first trimester of pregnancy. They ascertained the race of both partners: black/black in 149 cases, white/white in 129, white female/black male in 35, and black female/white male in 12.

The rate of bacterial vaginosis was 26.2 percent among white women and 45.3 percent among black women. Women from couples in which one or both partners are black were roughly twice as likely to develop bacterial vaginosis than women from couples in which both partners are white.

Simhan was not surprised that male partners contributed to the risk. However, "that paternal race was as powerful a factor as maternal race was unexpected," he said.

He and his colleagues speculate that the male contribution to bacterial vaginosis may be due to environmental factors, such as circumcision status or a man's genital bacteria. They also theorize that "immune discordance between the male and female partner may contribute to risk."

Simhan emphasized that the study did not extend to include birth outcomes. "We and others have other work suggesting that paternal race may be important in terms of preterm birth as well, so our report should not be considered by itself, but in terms of the broader public health implications."