Chapter 11. Bacterial Vaginosis

• • Grayish-white vaginal discharge.
• • Presence of vaginal epithelial clue cells.
• • Vaginal pH higher than 4.5.
• • Positive “whiff” test.
• • Decreased numbers of lactobacilli.
• • Increased bacteria count, consisting mainly of short rods observed on wet mount.

Bacterial vaginosis is the most frequent cause of vaginal discharge in the United States. Symptoms include vaginal discharge and odor, but half of women with bacterial vaginosis are asymptomatic. Previously given little attention and called nonspecific vaginitis or Gardnerella vaginitis, bacterial vaginosis is now known to be significantly associated with complications of pregnancy, including preterm rupture of membranes, preterm delivery, and low birth weight. Additionally, it has been associated with gynecologic complications such as postabortal endometritis, posthysterectomy vaginal cuff cellulitis, pelvic inflammatory diseases (PID), and urinary tract infections. It also appears to be a risk factor for acquisition of sexually transmitted diseases (STDs), including HIV.

The pathogenesis of bacterial vaginosis remains obscure, but the bulk of the epidemiologic data suggests that the disease is sexually transmitted. However, understanding of transmission is limited because the causative agent remains unknown and there is no clinical correlate of infection or disease in men. In terms of the microbiologic findings in bacterial vaginosis, lactobacilli, especially hydrogen peroxide—producing strains, are greatly diminished and are replaced with large numbers of Gardnerella vaginalis as well as multiple types of anaerobic bacteria and mycoplasmas. The decline in lactobacilli, which produce lactic acid, a key component in the maintenance of the normally low vaginal pH, results in increased vaginal pH. That increase in pH allows for the overgrowth of anaerobic bacteria, which apparently coat epithelial cells (“clue cells”) and produce a grayish-white vaginal discharge. The metabolites from anaerobic bacteria are rich in amines responsible for the characteristic fishy odor.

The use of condoms appears to be protective against acquisition of bacterial vaginosis. Although bacterial vaginosis may be an STD, antimicrobial therapy directed at anaerobic bacteria (eg, metronidazole) of the male partner has yet to be proved effective. Among women who have sex with women, examination and treatment of the sex partner is likely to be of benefit in preventing recurrence in the index case, because studies have found high concordance rates of bacterial vaginosis among sex partners in this setting. Twice-weekly prophylactic use of intravaginal metronidazole has proven to be efficacious in preventing recurrences.

Symptoms and Signs

Symptomatic bacterial vaginosis causes vaginal discharge or odor, or both. The odor is usually described as fishy and may be more noticeable after unprotected intercourse or during menses. Half of women with bacterial vaginosis complain of no symptoms. On examination, a homogenous, milky discharge adherent to the walls of the vagina may be present.

Laboratory Findings

Because a single etiologic agent has not been identified, clinical criteria (Amsel criteria) are used to make the diagnosis. According to these criteria, bacterial vaginosis is present if three of the following findings are present: (1) elevated vaginal pH (>4.5), (2) positive amine odor when vaginal fluid is mixed with 10% potassium hydroxide (KOH)—the so-called “whiff” test, (3) presence of clue cells (squamous epithelial cells covered with adherent bacteria) in a saline (wet mount) preparation of the vaginal fluid, and (4) homogenous vaginal discharge.

When examining vaginal fluid under the microscope, the morphotypes of the bacteria should also be noted. For example, if only Lactobacillus morphotypes are present (moderately long rods) it is unlikely that the patient has bacterial vaginosis. On the other hand, motile curved rods that represent Mobiluncus are highly suggestive of bacterial vaginosis. White blood cells usually are not present in the vaginal fluid of a patient infected only with bacterial vaginosis; their presence in the vaginal fluid should alert the clinician to the possibility of coinfection in either the vagina or the cervix.

Special Tests

Gram Stain

Gram stain is a reliable means of diagnosing bacterial vaginosis and has the advantage of being a permanent record that can be reviewed. Standardized criteria have been developed that facilitate interpretation, resulting in good intra- and interobserver reproducibility. In a multicenter study comparing the vaginal Gram stain with the Amsel criteria, the sensitivity and specificity of the Gram stain were found to be 89% and 83%, respectively. With Gram stain considered as the “gold standard,” the sensitivity and specificity of the Amsel criteria were 70% and 94%, respectively, suggesting that the use of the Amsel criteria may lead to underdiagnosis of bacterial vaginosis. Although the vaginal Gram stain is generally used in research settings, it is also offered in some clinical laboratories.

Other Diagnostic Tests

The following point-of-care tests for bacterial vaginosis are also available: (1) a rapid card test for detection of pH and amines; (2) detection of proline aminopeptidase in the vaginal fluid; (3) a rapid colorimetric test for sialidase, an enzyme that is elevated in bacterial vaginosis; and (4) an oligonucleotide probe technique based on high concentrations of G vaginalis (see Table 11–1). The first three tests are useful for initial screening but will not rule out mixed infections.

Other causes of vaginal complaints include yeast vaginitis, trichomoniasis, atrophic vaginitis, and other miscellaneous conditions. Vaginal complaints should never be diagnosed without analyzing objective laboratory data except, perhaps, in the case of recurrent infections that have been previously documented.

Bacterial vaginosis is associated with obstetric and gynecologic complications. In cross-sectional studies, bacterial vaginosis is a risk factor for preterm birth and low birth weight. However, prospective treatment studies have yielded inconsistent results as to the benefit of screening and treating for bacterial vaginosis in pregnancy. Gynecologic complications include postoperative infections following gynecologic surgery; acquisition of STDs, including PID; acquisition and transmission of HIV; and recurrent urinary tract infections. Screening and treating for bacterial vaginosis prior to elective gynecologic procedures is recommended. The leading hypothesis for the association of bacterial vaginosis with STDs and HIV is that the absence of protective hydrogen peroxide–producing lactobacilli found in patients with bacterial vaginosis precedes and facilitates the acquisition of these infections. Women with bacterial vaginosis should be screened for STDs at appropriate intervals. Screening for bacterial vaginosis in asymptomatic women is not generally recommended. Some experts recommend screening in pregnant women with a history of adverse pregnancy outcomes, but the data supporting the benefit of screening and treatment in that population are limited.

Options for treatment include both oral and topical metronidazole and clindamycin. Oral metronidazole should be administered at a dose of 500 mg twice daily for 7 days. The 2-g one-time-only dose used for trichomoniasis is not efficacious for bacterial vaginosis. Metronidazole may be used in the first trimester of pregnancy. Meta-analyses have failed to document any adverse events associated with its use during pregnancy. Oral clindamycin is an additional option at a dose of 300 mg twice daily for 7 days.

Intravaginal medications are as efficacious for treating bacterial vaginosis as oral agents and do not produce systemic side effects, although local side effects such as vaginal yeast infections may occur. Options include metronidazole gel at bedtime for 5 nights, clindamycin cream at bedtime for 7 nights, clindamycin ovules for 3 days, and sustained-release clindamycin as a single dose. There is concern that topical agents may not be adequate therapy for pregnant patients, in whom upper tract colonization with bacterial vaginosis–associated bacteria may have occurred; however, no studies have addressed this issue specifically

Reconstitution of the vaginal flora with exogenous lactobacilli has been suggested as an adjunct to antibiotic therapy; however, this requires use of a human-derived strain for effective colonization and is not commercially available. Therapy with yogurt, lactobacilli suppositories, or acidifying agents has not been found to be useful.

The treatment of asymptomatic bacterial vaginosis is controversial and is currently not recommended, with the exception of screening and treating for the condition prior to elective gynecologic procedures as a means of decreasing postoperative infections.

Recurrent episodes of bacterial vaginosis are common, and up to 50% of cases may recur in 6 months. Some data are available on the prophylactic use of intravaginal metronidazole gel twice weekly at bedtime to prevent recurrent episodes. The consistent use of condoms also appears to be protective against recurrent bacterial vaginosis.

Women with recurrent bacterial vaginosis may be referred to a gynecologist or infectious disease specialist for additional management.

Cure rates with any of the recommended therapies are 70–80%, and recurrence rates are high. Many women have frequent recurrences.

• • The treatment of asymptomatic bacterial vaginosis is controversial and is currently not recommended, with the exception of screening and treating for the condition prior to elective gynecologic procedures as a means of decreasing postoperative infections.