March 6, 2025 – Men whose female sex partners get the itchy vaginal infection called bacterial vaginosis may also start being offered treatment for the condition. That’s because a new study has determined that the infection isn’t simply a women’s health issue but is actually a sexually transmitted disease.
The findings, published this week in The New England Journal of Medicine, mark a major shift in how bacterial vaginosis (BV) is understood and defined, challenging long-held views that it was not an STI. BV develops when there is an imbalance in vaginal bacteria, and research now confirms that sexual activity—particularly with new or multiple partners—can introduce or spread the bacteria that cause it.
Left untreated, bacterial vaginosis (BV) can increase the risk of getting other STDs, including HIV, and also increases the risk of problems during pregnancy and birth. It is the most common cause of vaginal discharge among women of reproductive age. Until now, there has been no way to prevent the infections.
One-third of women worldwide develop BV in their lifetime, and many repeatedly battle the infection, which in addition to itching and discharge can cause a fishy smell and burning during urination. More than half of women with BV experience a recurrence within three months after taking a weeklong course of oral antibiotics, the researchers noted.
Experts say the new findings were not surprising.
“We’ve suspected for a long time that it’s a sexually transmitted infection (STI) because it has a similar incubation period (after sex) to most STIs and is associated with the same risk factors as STIs like chlamydia, such as change in sexual partner and not using condoms,” said researcher Lenka Vodstrcil, PhD, deputy head of the Genital Microbiota and Mycoplasma Group at Monash University’s Melbourne Sexual Health Centre, in a news release.
The study included 164 couples in Australia. The women all had BV infections and were in monogamous relationships with male partners. Researchers randomly assigned the couples to follow either traditional treatment (antibiotic for the woman only) or for the woman and the man to take antibiotics, plus for the man to apply a topical antimicrobial cream to the penile skin twice daily for seven days.
The research trial was halted early by a research safety oversight panel because it was evident that treating the woman only was inferior to treating both partners. The recurrence rate was 65% among women whose partners weren’t treated and 35% among women whose partners were treated.
Some treated men did report side effects, including nausea, headache, and metallic taste.
“Part of the difficulty in establishing whether BV is sexually transmitted has been that we still don’t know precisely which bacteria are the cause but advances in genomic sequencing are helping us close in on that mystery,” said fellow researcher Catriona Bradshaw, PhD.
In an editorial published alongside the research results, a pair of infectious disease experts said the evidence that the associated bacteria are transmitted sexually represents a paradigm shift.
The findings “also signify a need for a major change to the treatment approach of women with bacterial vaginosis with respect to how women should be counseled regarding the origin of their infection and to the need to engage their male partners in sharing responsibility for transmission and treatment,” the editorial authors wrote. “To date, there have been no effective strategies to prevent sexual transmission of bacterial vaginosis–associated bacteria, apart from consistent use of condoms.”
