A new study adds to evidence that bacterial vaginosis, the most common vaginal infection in women of childbearing age, is a sexually transmitted disease.

Bacterial vaginosis, or BV, occurs when the normal balance of “good” and “bad” bacteria in the vagina is upset. While certain sexual risk factors, like having multiple partners, have been linked to BV, the role of sexual activity in BV transmission has not been completely clear.

A few decades ago, researchers believed that BV was largely a sexually transmitted disease (STD). But a number of studies since then have questioned that belief.

One problem is that there is still uncertainty about which pathogen causes BV; another is that studies have found the infection among “virginal” women as well as sexually experienced women.

In the past several years, however, the thinking on BV has seesawed again. Research showing the importance of condom use and the number of sexual partners in BV risk has given new weight to the idea that BV is an STD.

In this latest study, Australian researchers found that of 528 college women they tested, none of those with no sexual experience at all - intercourse or any other form of sexual activity - had BV.

In contrast, the infection was found in 6 percent of women who’d had intercourse, and in 4 percent of those who reported other forms of sexual activity, including oral sex and hand-genital contact.

What’s more, the risk of having BV increased with the number of sexual partners a woman had had in the past year. Those who had had intercourse with more than three partners were seven times more likely to have BV than women who reported fewer partners.

The findings suggest that while the pathogen or pathogens causing BV are not firmly established, “it does appear, on the balance of probabilities, that BV is likely to be a sexually transmitted condition,” lead researcher Dr. Katherine A. Fethers, of the Melbourne Sexual Health Centre in Victoria, told Reuters Health in an email.

The implication for women, according to the researcher, is that BV can be prevented.

“We know that increased numbers of partners and lack of condom use are associated with BV,” Fethers said, “so we can generate some preventative messages from this evidence.”

“We would currently recommend condom use for women to reduce the risk of BV,” she said.

As for research showing that BV is sometimes seen in virgins, Fethers and her colleagues point out that two widely cited studies failed to collect information on sexual activity other than intercourse.

Research shows that certain STDs, including herpes and human papillomavirus (HPV), can be transmitted through sexual activity other than intercourse.

Symptoms of BV include discharge, odor, itching and burning during urination - though women often have no symptoms at all. BV usually causes no serious problems, but the infection can make women more vulnerable to contracting HIV or other STDs. BV infection during pregnancy can raise the risk of certain complications, such as preterm delivery.

The infection can clear up on its own; however, experts recommend antibiotic treatment for all women with BV in order to prevent complications.

SOURCE: Journal of Infectious Diseases, December 1, 2009.