A new study adds to growing evidence that bacterial vaginosis (BV) and sexually transmitted infections (STIs) often occur together. The findings support testing anyone with vaginal symptoms for BV, yeast infections, and common STIs at the same time because they may have more than one infection.

The study was conducted by researchers from Quest Diagnostics (which operates a network of laboratories across the country) and Hologic, Inc. (which makes some of the diagnostic equipment those laboratories use). It was published in Obstetrics and Gynecology Open.

BV Associated with STIs, But Not Yeast Infections

Researchers looked at test results of more than 1.5 million women who were tested for BV, vulvovaginal candidiasis (VVC, commonly known as a yeast infection), chlamydia, gonorrhea, trichomoniasis (trich), and Mycoplasma genitalium (mgen) between 2022 and 2024. (Like chlamydia and gonorrhea, mgen is a bacterial STI that can infect the cervix, the urethra, or the rectum.)

Overall, 39% of participants tested positive for BV, 29% for VVC, and 11% tested positive for both conditions. About 12% of the women with BV also tested positive for at least one STI, compared to fewer than 4% of women without the condition.

Compared with women who did not have BV, women with BV were:

• Nearly three times more likely to have chlamydia.
• Almost four times more likely to have gonorrhea.
• More than three times more likely to have trich.
• Nearly twice as likely to have Mgen.

The researchers did not find the same pattern with VVC. Women who tested positive for a yeast infection alone were no more likely to have chlamydia, gonorrhea, or mgen than women who did not have a yeast infection. They were only slightly more likely to have trich. This suggests there may be something unique about BV that increases the likelihood of having an STI at the same time.

Understanding BV

BV is the most common cause of vaginal symptoms in women ages 15–44. It develops when the normal balance of “good” and “bad” bacteria in the vagina changes. BV is not considered an STI, but it is considered “sexually associated.” Sexual activity is one of thing that can change the balance of bacteria in the vagina. Taking antibiotics or douching can also upset this balance.

Common symptoms of BV include unusual vaginal discharge, a fishy odor, itching, irritation, and burning during urination. Of course, many STIs can cause similar symptoms. Because they feel the same, it’s usually not possible to tell what type of infection a person has based on symptoms alone. Also, some people don’t have any symptoms with either BV or STIs. This is why testing is so important.

BV, yeast infections can all be treated and so can chlamydia, gonorrhea, trich, and mgen, but they require different medications. Moreover, as the study shows, people may have more than one infection at the same time. Getting the right treatment depends on getting the right tests. The good news is that many laboratory tests can detect BV, yeast infections, and some common STIs using a single vaginal swab. This makes testing much easier.

Why is there a connection between BV and STIs?

Researchers still don’t know exactly why BV and STIs are so often found together. One theory is that the changes in the balance of bacteria that cause BV also make it easier for the germs that cause STIs to infect the area. Other research has suggested that some types of BV may be more strongly linked to chlamydia than others, but scientists are still working to understand exactly how these conditions are connected. Learning more about this relationship could help researchers find better ways to prevent BV in the future.

In the meantime, this study highlights the overlap between BV and STIs and reminds us of the importance of comprehensive testing.