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Bacterial Vaginosis

Vaginitis is usually characterized by a vaginal discharge or by vulvar itching and irritation; a vaginal odor may be present. The three diseases most frequently associated with vaginal discharge are trichomoniasis (caused by T. vaginalis), Bacterial Vaginosis (BV) (caused by a replacement of the normal vaginal flora by an overgrowth of anaerobic microorganisms and Gardnerella vaginalis), and candidiasis (usually caused by Candida albicans). Vulvovaginal candidiasis usually is not transmitted sexually, but it is included in this section because it is often diagnosed in women being evaluated for sexually transmitted diseases.

Vaginitis is diagnosed by pH and microscopic examinations of fresh samples of the discharge. The pH of the vaginal secretions can be determined by narrow-range pH paper for the elevated pH typical of BV or trichomoniasis (i.e., a pH of greater than 4.5). One way to examine the discharge is to dilute a sample in one or two drops of 0.9% normal saline solution on one slide and 10% potassium hydroxide (KOH) solution on a second slide. An amine odor detected immediately after applying KOH suggests BV. A cover slip is placed on each slide and examined under a microscope at low- and high-dry power. The motile T. vaginalis or the clue cells of BV usually are identified easily in the saline specimen. The yeast or pseudohyphae of Candida species are more easily identified in the KOH specimen. The presence of objective signs of vulvar inflammation in the absence of vaginal pathogens, along with a minimal amount of discharge, suggests the possibility of mechanical, chemical, allergic, or other noninfectious irritation of the vulva. Culture for T. vaginalis is more sensitive than microscopic examination. Laboratory testing fails to identify the cause of vaginitis among a substantial minority of women.

Bacterial Vaginosis

Bacterial vaginosis (BV) is the most common cause of vaginitis symptoms among women of childbearing age. BV–previously called nonspecific vaginitis or Gardnerella-associated vaginitis–can be transmitted through sexual activity, although the organisms responsible have been found in young women who are not sexually active, as well. BV is due to a change in the balance among different types of bacteria in the vagina. Instead of the normal predominance of Lactobacillus bacteria, increased numbers of organisms such as Gardnerella vaginalis, Bacteroides, Mobiluncus, and Mycoplasma hominis are found in the vagina in women with BV. Investigators are studying the role that each of these microbes may play in causing BV. The role of sexual activity in the development of BV is not understood. Additionally, intrauterine devices (IUDs) may increase the risk of acquiring bacterial vaginosis.

Diagnostic Considerations

BV can be diagnosed by the use of clinical or Gram stain criteria. Clinical criteria require three of the following symptoms or signs:

  • A homogeneous, white, non-inflammatory discharge that smoothly coats the vaginal walls;
  • The presence of clue cells on microscopic examination;
  • A pH of vaginal fluid greater than 4.5;
  • A fishy odor of vaginal discharge before or after addition of 10% KOH (i.e., the whiff test).

When a Gram stain is used, determining the relative concentration of the bacterial morphotypes characteristic of the altered flora of BV is an acceptable laboratory method for diagnosing BV. Culture of G. vaginalis is not recommended as a diagnostic tool because it is not specific.


The principal goal of therapy for BV is to relieve vaginal symptoms and signs of infection. All women who have a symptomatic disease require treatment, regardless of pregnancy status.

BV during pregnancy is associated with adverse pregnancy outcomes. The results of several investigations indicate that treatment of pregnant women who have BV and who are at high risk for pre-term delivery (i.e., those who previously delivered a premature infant) might reduce the risk for pre-maturity. Therefore, high-risk pregnant women who do not have symptoms of BV may be evaluated for treatment.

Although some experts recommend treatment for high-risk pregnant women who have asymptomatic BV, others believe more information is needed before such a recommendation is made. A large, randomized clinical trial is underway to assess treatment for asymptomatic BV in pregnant women; the results of this investigation should clarify the benefits of therapy for BV in women at both low and high risk for pre-term delivery.

The bacterial flora that characterizes BV has been recovered from the endometria and salpinges of women who have PID. BV has been associated with endometritis, PID, and vaginal cuff cellulitis after invasive procedures such as endometrial biopsy, hysterectomy, hysterosalpingography, and placement of an intrauterine device, cesarean section, and uterine curettage. The results of one randomized controlled trial indicated that treatment of BV with metronidazole substantially reduced post-abortion PID. On the basis of these data, consideration should be given to treatment of women who have symptomatic or asymptomatic BV before surgical abortion procedures are performed. However, more information is needed before recommending whether or not patients who have asymptomatic BV should be treated before other invasive procedures are performed.

Recommended Regimens for Non-Pregnant Women

For treatment of pregnant women, see Bacterial Vaginosis, Special Considerations, Pregnancy.

  • Metronidazole 500 mg orally twice a day for 7 days, or
  • Clindamycin cream 2%, one full applicator (5 g) intra-vaginally at bedtime for 7 days, or
  • Metronidazole gel 0.75%, one full applicator (5 g) intra-vaginally twice a day for 5 days.

NOTE: Patients should be advised to avoid consuming alcohol during treatment with metronidazole and for 24 hours thereafter. Clindamycin cream is oil-based and might weaken latex condoms and diaphragms. Refer to condom product labeling for additional information.

Alternative Regimens

  • Metronidazole 2 g orally in a single dose, or
  • Clindamycin 300 mg orally twice a day for 7 days.

Metronidazole 2-g single-dose therapy is an alternative regimen because of its lower efficacy for BV. Oral metronidazole (500 mg twice a day) is efficacious for the treatment of BV, resulting in relief of symptoms and improvement in clinical course and flora disturbances. Based on efficacy data from four randomized controlled trials, overall cure rates 4 weeks after completion of treatment did not differ significantly between the 7-day regimen of oral metronidazole and the clindamycin vaginal cream (78% vs. 82%, respectively). Similarly, the results of another randomized controlled trial indicated that cure rates 7 to 10 days after completion of treatment did not differ significantly between the 7-day regimen of oral metronidazole and the metronidazole vaginal gel (84% vs. 75%, respectively). FDA has approved Flagyl ER (TM) (750 mg) once daily for 7 days for treatment of BV is also an option.

Some healthcare providers remain concerned about the possible teratogenicity of metronidazole, which has been suggested by experiments using extremely high and prolonged doses in animals. However, a recent meta-analysis does not indicate teratogenicity in humans. Some healthcare providers prefer the intra-vaginal route because of a lack of systemic side effects (e.g., mild-to-moderate gastrointestinal disturbance and unpleasant taste). Mean peak serum concentrations of metronidazole after intra-vaginal administration are less than 2% the levels of standard 500-mg oral doses, and the mean bioavailability of clindamycin cream is approximately 4%.


Follow-up visits are unnecessary if symptoms resolve. Recurrence of BV is not unusual. Because treatment of BV in high-risk pregnant women who are asymptomatic might prevent adverse pregnancy outcomes, a follow-up evaluation, at 1 month after completion of treatment, should be considered to evaluate whether or not therapy was successful. The alternative BV treatment regimens may be used to treat recurrent disease. No long-term maintenance regimen with any therapeutic agent is recommended.

Management of Sex Partners

The results of clinical trials indicate that a woman’s response to therapy and the likelihood of relapse or recurrence are not affected by treatment of her sex partner(s). Therefore, routine treatment of sex partners is not recommended.

Special Considerations

Clindamycin cream is preferred in case of allergy or intolerance to metronidazole. Metronidazole gel can be considered for patients who do not tolerate systemic metronidazole. Patients allergic to oral metronidazole should not be administered metronidazole vaginally.


BV has been associated with adverse pregnancy outcomes (e.g., premature rupture of the membranes, pre-term labor, and pre-term birth). The organisms found in increased concentration in BV also are frequently present in postpartum or post-cesarean endometritis. Because treatment of BV in high-risk pregnant women (i.e., those who have previously delivered a premature infant) who are asymptomatic might reduce pre-term delivery, such women may be screened and those with BV can be treated. The screening and treatment should be conducted at the earliest part of the second trimester of pregnancy. The recommended regimen is metronidazole 250 mg orally three times a day for 7 days. The alternative regimens are metronidazole 2 g orally in a single dose or clindamycin 300 mg orally twice a day for 7 days.

Low-risk pregnant women (i.e., women who previously have not had a premature delivery) who have symptomatic BV should be treated to relieve symptoms. The recommended regimen is metronidazole 250 mg orally three times a day for 7 days. The alternative regimens are metronidazole 2 g orally in a single dose; clindamycin 300 mg orally twice a day for 7 days; or metronidazole gel, 0.75%, one full applicator (5 g) intra-vaginally, twice a day for 5 days. Some experts prefer the use of systemic therapy for low-risk pregnant women to treat possible sub-clinical upper genital tract infections.

Lower doses of medication are recommended for pregnant women to minimize exposure to the fetus. Data are limited concerning the use of metronidazole vaginal gel during pregnancy. The use of clindamycin vaginal cream during pregnancy is not recommended, because two randomized trials indicated an increase in the number of pre-term deliveries among pregnant women who were treated with this medication.

Thomas G. Stovall, M.D.
Dr. Stovall is a Clinical Professor of Obstetrics and Gynecology at the University of Tennessee Health Science Center in Memphis, Tennessee and Partner of Women’s Health Specialists, Inc.