Bacterial vaginosis (BV) has been considered a bacterial imbalance in the vagina, rather than a sexually transmitted infection (STI). New research is challenging this assumption.

A study published in the New England Journal of Medicine suggests that BV, a common vaginal infection in women, may be transmitted sexually. The findings indicate that treating male partners alongside women is necessary to cure both partners and reduce the risk of reinfection.

In addition to discomfort and a “fishy” odor, BV can lead to serious health complications, including newborn deaths, premature births, infertility, an increased risk of HIV and other STIs, and pelvic inflammatory disease.

More than half of women who receive the standard one-week oral antibiotic treatment experience a recurrence within three months.

To test whether treating male partners could improve outcomes, researchers in Australia studied 164 monogamous couples. Half of the couples followed the standard approach, where only the woman received a seven-day course of antibiotics. The other half received treatment for both partners, with the men taking a seven-day course of oral antibiotics and applying a topical antibiotic to the penis.

After 12 weeks, BV recurred in 35% of women whose partners were also treated, compared to 63% of those who were treated alone.

“This successful intervention is relatively cheap and short and has the potential for the first time to not only improve BV cure for women, but opens up exciting new opportunities for BV prevention, and prevention of the serious complications associated with BV,” said Catriona Bradshaw, PhD, a co-author of the study and a clinical researcher at the Melbourne Sexual Health Centre.

What the Study Found

A key question posed by the study is whether BV should be considered an STI. Defining BV as an STI would make it more likely for healthcare providers to consider partners of women who get BV as well.

“[BV] 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,” Lenka Vodstrcil, PhD, an author of the study and a senior research fellow at the Melbourne Sexual Health Centre, said in a statement.

Bradshaw said while studies have shown that men may harbor bacteria associated with BV on the penile skin and inside the penis, previous trials that included male partners did not show improved cure rates in their female partners.

“This was interpreted as evidence against sexual transmission,” Bradshaw said. “However, these studies had design limitations, and none used a combination of oral and topical antibiotics to adequately clear BV bacteria in men, especially from the penile-skin site.”

The new study shows that women can get reinfection from their partner and offers evidence that BV is in fact an STI, Bradshaw added. However, researchers still don’t know precisely which bacteria cause BV, although genomic sequencing is getting close to unlocking this mystery.

Is BV Sexually Transmitted?

While the study shows that treating male partners can be effective at preventing reinfection, it doesn’t prove that BV is sexually transmitted, according to Alessandra Hirsch, MD, assistant professor of obstetrics and gynecology at Columbia University Vagelos College of Physicians and Surgeons, who is unaffiliated with the study.

“BV can arise from a number of situations that do not have to do with sex. Some women get BV every time they are treated for a yeast infection,” Hirsch told Verywell.

Hirsch said there’s already shame surrounding BV, and categorizing BV as an STI may further stigmatize the condition. The study also focused only on heterosexual couples, but recurrent BV can affect gay women and pregnant people who are not having sex as well, she added.

“We have work to do as a medical community to destigmatize STIs in general,” Hirsch said. “In the meantime, let’s not add to the panic and fray. Treating a male partner with oral and topical medicine in a woman with recurrent bacterial vaginosis makes good clinical sense based on this study. Let’s leave it at that.”

Will This Change Treatment Guidelines for BV?

Clinicians at the Melbourne Sexual Health Centre have already changed their guidelines to treat both partners if a woman in a monogamous relationship is diagnosed with BV. The same change may not take place in the United States just yet.

“Because this paper is so recent, and institutional guidelines can take time to change, each physician can make their own decision about how to incorporate new research into their practice,” Hirsch said.

U.S. providers generally follow guidelines from the American College of Obstetricians and Gynecologists (ACOG) and the Centers for Disease Control and Prevention (CDC) when prescribing medications for gynecologic infections.

Neither ACOG nor CDC has replied to queries from Verywell about whether the study might result in a change to the current treatment guidelines for BV.

Hirsch said doctors in the U.S. would likely use the same first-line BV medications—metronidazole and clindamycin gel—to treat male partners.

“They are well-established, older drugs, and overall considered quite safe,” she said.