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Bacterial Vaginosis

Healthy vaginal flora is comprised of more than 90% lactobacilli. Lactobacillus species play a key role in maintaining balance and host defense against pathogens by producing several substances that inhibit the growth of deleterious microorganisms. Lactobacillus species inhibit the growth of pathogenic bacteria by generating hydrogen peroxide, which disrupts bacterial membranes, and by producing lactic acid, which maintain a highly acidic environment.

Bacterial vaginosis (BV) is a common lower genital tract infection caused by a disruption of the normal microbiological environment. BV occurs when lactobacilli are depleted and replaced by a 1,000-fold increase in the number of anaerobic bacteria such as the Gardnerella, Prevotella, and Atopobium species. BV is usually asymptomatic and can resolve spontaneously. When symptoms occur, they include an off-white, thin, homogenous discharge or a vaginal “fishy” odor. More than 50% of women with symptomatic infections have a recurrence within 12 months.

BV occurs in as many as 29% of women between the ages of 14 and 49 years in the United States and in 5.8% to 19.3% of pregnant women. Prevalence varies with race and ethnicity. Rates as high as 52% have been reported in African American women, 32% in Mexican Americans and 23% in non-Hispanic whites. Certain sexual behaviors increase the risk BV including a high number of partners, lack of condom or contraceptive use, vaginal sex, sex with a female partner, and concurrent sexually transmitted infections. Women who have bacterial vaginosis are at increased risk for infection with herpes simplex virus type 2, Trichomonas vaginalis, Neisseria gonorrhoeae, Chlamydia trachomatis, and human immunodeficiency virus (HIV).

BV during pregnancy has been associated with adverse obstetrical outcomes including preterm delivery, early miscarriage, recurrent pregnancy loss, pelvic inflammatory disease, postpartum endometritis, and low birth weight infants. Most clinicians treat symptomatic BV in pregnancy. The American College of Obstetrics and Gynecology and the United States Preventive Services Task Force do not recommend screening of asymptomatic pregnant women for BV.

A clinical diagnosis is made with Amsel’s clinical criteria by fulfilling three of four criteria:

  • Vaginal pH greater than 4.5
  • Presence of clue cells on wet mount microscopy
  • Thin homogeneous discharge,
  • A fishy odor when potassium hydroxide is added to vaginal secretions.

Nucleic acid assays are available for detection of BV associated bacterial species. These assays also detect nonvaginosis organisms such as Trichomonas vaginalis and Candida species. The BD Affirm Vaginal Panel III uses a nonamplified DNA probe specific to Gardnerella vaginalis. Sensitivity for BV is 87% and specificity is 81%.

BD MAX Vaginal Panel is a multiplex polymerase chain reaction (PCR) assay that tests for five vaginosis-associated organisms: Lactobacillus species, Gardnerella vaginalis, Atopobium vaginae, Bacterial Vaginosis Associated Bacteria-2 (BVAB- 2), and Megasphaera-1. BD Max sensitivity is 93% and specificity is 92%.

OSOM® BVBLUE® (Sekisui Diagnostics, Burlington, MA) is an FDA approved test detects elevated vaginal fluid sialidase activity associated with vaginosis. VS-Sense-Pro is an FDA approved test that detects alterations in vaginal pH.

Oral metronidazole and oral clindamycin, as well as vaginal metronidazole gel or clindamycin cream, are the usual treatments for symptomatic BV.


Kenyon C, Colebunders R, Crucitti T. The global epidemiology of bacterial vaginosis: a systematic review. Am J Obstet Gynecol. 2013;209(6):505-523.

American Academy of Physicians. Clinical preventive service recommendation: bacterial vaginosis.

USPSTF, Screening for Bacterial Vaginosis in Pregnant Adolescents and Women to Prevent Preterm Delivery: An Updated Systematic Review for the U.S. Preventive Services Task Force, October 2019, AHRQ Publication No. 19-05259-EF-1

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