Merck Manual

Please confirm that you are a health care professional

honeypot link

Bacterial Vaginosis (BV)


Oluwatosin Goje

, MD, MSCR, Cleveland Clinic, Lerner College of Medicine of Case Western Reserve University

Last full review/revision Apr 2021| Content last modified Apr 2021
Click here for Patient Education
Topic Resources

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. Diagnosis is confirmed by testing vaginal secretions. Treatment is usually with oral or topical metronidazole or topical clindamycin.

Anaerobic pathogens that overgrow include Prevotella species, Peptostreptococcus species, Gardnerella vaginalis, Mobiluncus species, and Mycoplasma hominis, which increase in concentration by 10- to 100-fold and replace the normally protective lactobacilli.

Risk factors for bacterial vaginosis include those for sexually transmitted diseases Overview of Sexually Transmitted Diseases Sexually transmitted diseases (STDs), also termed sexually transmitted infections (STIs), can be caused by a number of microorganisms that vary widely in size, life cycle, the diseases and symptoms... read more . 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 Pelvic Inflammatory Disease (PID) Pelvic inflammatory disease (PID) is a polymicrobial infection of the upper female genital tract: the cervix, uterus, fallopian tubes, and ovaries; abscess may occur. PID may be sexually transmitted... read more , postabortion and postpartum endometritis Puerperal Endometritis Puerperal endometritis is uterine infection, typically caused by bacteria ascending from the lower genital or gastrointestinal tract. Symptoms are uterine tenderness, abdominal or pelvic pain... read more , posthysterectomy vaginal cuff infection, chorioamnionitis Intra-Amniotic Infection Intra-amniotic infection is infection of the chorion, amnion, amniotic fluid, placenta, or a combination. Infection increases risk of obstetric complications and problems in the fetus and neonate... read more , premature rupture of membranes Prelabor Rupture of Membranes (PROM) Prelabor rupture of membranes is leakage of amniotic fluid before onset of labor. Diagnosis is clinical. Delivery is recommended when gestational age is ≥ 34 weeks and is generally indicated... read more , preterm labor Preterm Labor Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more , and preterm birth Premature Infants An infant born before 37 weeks gestation is considered premature. Prematurity is defined by the gestational age at which infants are born. Previously, any infant weighing read more .

General reference

  • 1. Muzny CA, Schwebke JR: Pathogenesis of bacterial vaginosis: Discussion of current hypotheses. J Infect Dis 214 (Suppl 1):S1–S5, 2016. doi: 10.1093/infdis/jiw121

Symptoms and Signs of Bacterial Vaginosis

Vaginal discharge due to bacterial vaginosis 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, irritation, erythema, and edema are not common.

Diagnosis of Bacterial Vaginosis

  • Clinical criteria

  • Vaginal pH and wet mount

For bacterial vaginosis to be diagnosed, 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 white blood cells on a saline wet mount suggests a concomitant infection (possibly trichomonal, gonorrheal, or chlamydial cervicitis Cervicitis Cervicitis is infectious or noninfectious inflammation of the cervix. Findings may include vaginal discharge, vaginal bleeding, and cervical erythema and friability. Women are tested for infectious... read more Cervicitis ) and the need for additional testing.

Diagnosis references

  • 1. Cartwright CP, Lembke BD, Ramachandran K, et al: Development and validation of a semiquantitative, multitarget PCR assay for diagnosis of bacterial vaginosis. J Clin Microbiol 50 (7):2321–2329, 2012. doi: 10.1128/JCM.00506-12 Epub 2012 Apr 25.

  • 2. Schwebke JR, Gaydos CA, Nyirjesy P, et al: Diagnostic performance of a molecular test versus clinician assessment of vaginitis. J Clin Microbiol 56 (6):e00252-18, 2018. doi: 10.1128/JCM.00252-18 Print 2018 Jun.

  • 3. Gaydos CA, Beqaj S, Schwebke JR, et al: Clinical validation of a test for the diagnosis of vaginitis. Obstet Gynecol 130 (1):181–189, 2017. doi: 10.1097/AOG.0000000000002090

  • 4. Coleman JS, Gaydos CA: Molecular diagnosis of bacterial vaginosis: An update. J Clin Microbiol 56 (9):e00342–e00318, 2018. doi: 10.1128/JCM.00342-18 Print 2018 Sep.

Treatment of Bacterial Vaginosis

  • Metronidazole or clindamycin

The following treatments for bacterial vaginosis are equally effective:

  • Oral metronidazole 500 mg twice a day for 7 days or 2 g once

  • Metronidazole 0.75% gel 5 g (one applicator full) intravaginally once a day for 7 days

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

Oral metronidazole 500 mg twice a day 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.

When treated, symptomatic bacterial vaginosis usually resolves in a few days but commonly recurs. If it recurs often, antibiotics may have to be taken for a long time.

Treatment references

  • 1. Schwebke JR, Morgan FG Jr, Koltun W, Nyirjesy P: A phase-3, double-blind, placebo-controlled study of the effectiveness and safety of single oral doses of secnidazole 2 g for the treatment of women with bacterial vaginosis. Am J Obstet Gynecol 217 (6):678.e1–678.e9, 2017. doi: 10.1016/j.ajog.2017.08.017 Epub 2017 Sep 1.

  • 2. Hillier SL, Nyirjesy P, Waldbaum AS, et al: Secnidazole treatment of bacterial vaginosis: A randomized controlled trial. Obstet Gynecol 130 (2):379-386, 2017. doi: 10.1097/AOG.0000000000002135

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read
Test your knowledge
Management of Normal Delivery
Options for pain management during normal delivery include regional, local, and general anesthesia. Of these types of anesthesia, which of the following is a safe and simple method for uncomplicated spontaneous vaginal deliveries in women who wish to bear down and push?
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest