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Bacterial Vaginosis (BV)

By David E. Soper, MD, J. Marion Sims Professor, Department of Obstetrics and Gynecology, Medical University of South Carolina

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Bacterial vaginosis is vaginitis due to a complex alteration of vaginal flora in which lactobacilli decrease and anaerobic pathogens overgrow. Symptoms include a gray, thin, fishy-smelling vaginal discharge and itching. Diagnosis is confirmed by testing vaginal secretions. Treatment is usually with oral or topical metronidazole or topical clindamycin.

Bacterial vaginosis is the most common infectious vaginitis. The cause is unknown. Anaerobic pathogens that overgrow include Prevotella sp, Peptostreptococcus sp, Gardnerella vaginalis, Mobiluncus sp, and Mycoplasma hominis, which increase in concentration by 10- to 100-fold and replace the normally protective lactobacilli.

Risk factors include those for sexually transmitted diseases (see Overview of Sexually Transmitted Diseases). In women who have sex with women, risk increases as the number of sex partners increases. However, bacterial vaginosis can occur in virgins, and treating the male sex partner does not appear to affect subsequent incidence in sexually active heterosexual women. Use of an intrauterine device is also a risk factor.

Bacterial vaginosis appears to increase the risk of pelvic inflammatory disease, postabortion and postpartum endometritis, posthysterectomy vaginal cuff infection, chorioamnionitis, premature rupture of membranes, preterm labor, and preterm birth.

Symptoms and Signs

Vaginal discharge is malodorous, gray, and thin. Usually, a fishy odor is present, often becoming stronger when the discharge is more alkaline—after coitus and menses. Pruritus and irritation are common. Erythema and edema are uncommon.


  • Clinical criteria

  • Vaginal pH and wet mount

For the diagnosis, 3 of 4 criteria must be present:

  • Gray discharge

  • Vaginal secretion pH > 4.5

  • Fishy odor on the whiff test

  • Clue cells

Clue cells (bacteria adhering to epithelial cells and sometimes obscuring their cell margins) are identified by microscopic examination of a saline wet mount. Presence of WBCs on a saline wet mount suggests a concomitant infection (possibly trichomonal, gonorrheal, or chlamydial cervicitis) and the need for additional testing.


  • Metronidazole or clindamycin

(See also the Centers for Disease Control and Prevention practice guideline Sexually transmitted diseases characterized by vaginal discharge.)

The following treatments are equally effective:

  • Metronidazole 0.75% vaginal gel bid for 5 days

  • 2% clindamycin vaginal cream once/day for 7 days

  • Oral metronidazole 500 mg bid for 7 days or 2 g once

Oral metronidazole 500 mg bid for 7 days is the treatment of choice for patients who are not pregnant, but because systemic effects are possible with oral drugs, topical regimens are preferred for pregnant patients. Women who use clindamycin cream cannot use latex products (ie, condoms or diaphragms) for contraception because the drug weakens latex.

Treatment of asymptomatic sex partners is unnecessary.

For vaginitis during the 1st trimester of pregnancy, metronidazole vaginal gel should be used, although treatment during pregnancy has not been shown to lower the risk of pregnancy complications. To prevent endometritis, clinicians may give oral metronidazole prophylactically before elective abortion to all patients or only to those who test positive for bacterial vaginosis.

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