Essentials of Diagnosis
General Considerations
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.
Pathogenesis
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.
Prevention
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.
Clinical Findings
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.
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
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