Bacterial vaginosis (formerly gardnerella vaginitis) occurs when normal vaginal bacteria are replaced by unhealthy bacteria, including Gardnerella vaginalis.

Bacterial vaginosis (BV) is the most common bacterial vaginal infection and the leading cause of abnormal vaginal discharge and odor among women aged 15 to 44, according to the Centers for Disease Control and Prevention 6. Formerly known as gardnerella vaginitis, BV is believed to be initiated by infection with a species of bacteria called Gardnerella vaginalis (G. vaginalis). With BV, the normal bacteria that inhabit the vagina are largely replaced by G. vaginalis and other closely related bacteria 4. Although BV is often asymptomatic, it can increase a woman's risk for acquiring certain sexually transmitted diseases and the risk for some pregnancy complications. While BV remains incompletely understood, certain risk factors have been identified.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.

Role of Gardnerella

Bacteria normally live in the vagina, just as they do on the skin. Lactobacillus bacteria normally predominate in the vagina and keep the pH in a healthy range. When G. vaginalis infects the vagina, it tends to overgrow the normal bacteria, which enables other types of unhealthy bacteria to also increase to abnormal levels. This disrupts the normal bacterial balance and pH of the vagina, leading to BV and its associated symptoms.

Risk Factors

Sexual Activity

Any woman can develop BV, although infection with G. vaginalis is rare in women who are not sexually active. Although the link between sexual activity and BV remains incompletely understood, the risk for BV increases with a woman's lifetime and recent number of sexual partners (male or female). Engaging in sex with a new partner also appears to increase the risk for developing BV.

Sexual Partners and Practices

BV is not considered sexually transmitted infection per se. However, it does appear that a woman with BV can pass the infection to female sex partners, as reported in December 2015 in "PLoS One." The potential passage of G. vaginalis from men who harbor the bacteria to their female sex partners is less clear and research to date has been conflicting. Nonetheless, male condom use is associated with a reduced risk of developing BV 10. Use of hormone-based contraception also reduces BV risk. In contrast, douching seems to increase a woman's BV risk, possibly by altering the levels of normal vaginal bacteria. Receptive oral sex is also associated with increased BV risk.

Other Risk Factors

Other factors appear to increase a woman's risk for G. vaginalis infection and subsequent development of BV -- although the mechanisms are incompletely understood. These risk factors include cigarette smoking, recent antibiotic use and African ethnicity.

Warnings and Precautions

BV increases a woman's risk for acquiring HIV, gonorrhea, chlamydia, genital herpes and pelvic inflammatory disease. BV also increases the risk for pregnancy complications, including premature birth and delivering a low-birth-weight baby. Therefore, it's important to see your healthcare provider as soon as possible if you suspect you might have BV. Symptoms may include:

  • Increased watery vaginal discharge
  • Fishy or unpleasant vaginal discharge odor (especially after unprotected intercourse)
  • Itchiness, burning or soreness around the vaginal opening
  • Burning with urination

Reviewed and revised by: Tina M. St. John, M.D.