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.
(See also Overview of Vaginitis.)
Bacterial vaginosis is the most common infectious vaginitis. The pathogenesis is unclear but involves the overgrowth of multiple bacterial pathogens and a decrease in the usual lactobacillus-predominant vaginal flora (1).
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. 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.
- 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) and the need for additional testing.
Also, some relatively new diagnostic tests are commercially available for clinical use (1–4).
- 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.
- 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
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