Bacterial vaginosis: Clinical sciences

Bacterial vaginosis, or BV, is the most common cause of abnormal vaginal discharge. Keep in mind this is not a true infection but a dysbiosis, meaning an imbalance of the normal microorganisms in the vagina. This happens when the hydrogen peroxide and lactic acid producing Lactobacillus species are replaced by an overgrowth of anaerobes such as Gardnerella vaginalis and Prevotella species. The presence of BV can increase the risk of pelvic inflammatory disease and postprocedural gynecologic infections, as well as increase one’s susceptibility to sexually transmitted infections such as HIV, chlamydia and herpes simplex virus type-2, or HSV-2. In pregnancy, it is associated with prelabor rupture of membranes, preterm birth, intra-amniotic infections, and postpartum endometritis.

Your first step in evaluating a patient with a chief concern suggesting bacterial vaginosis is a focused history and physical exam. BV is often asymptomatic. However, patients might report a thin, watery, grayish-white discharge, and an unpleasant “fishy” vaginal odor. Many patients report increased symptoms during menses or after intercourse.

Be sure to ask about risk factors for BV, starting with a sexual history. BV is not sexually transmitted, but it’s associated with certain sexual behaviors, such as having a new partner, having multiple partners, having HSV-2 seropositivity, and not using a condom. On the other hand, BV rarely occurs in patients who have never been sexually active. Additionally, BV is more prevalent in those using a copper intrauterine device. Using other contraceptives won’t increase one’s risk, but hormonal contraception might even be protective against it. Finally, another important risk factor for BV involves certain hygiene practices such as vaginal douching and vulvar shaving.

Now, when performing a physical exam, you will find a thin grayish-white homogeneous vaginal discharge and an unpleasant “fishy” odor that results from volatile amines produced by the overgrowth of anaerobic bacteria. If you see these findings, suspect bacterial vaginosis.

So, if you suspect bacterial vaginosis, your next step is to obtain samples of the discharge from the vaginal walls and fornices. Evaluate the discharge with saline microscopy, particularly looking for clue cells and lactobacilli. Clue cells are epithelial cells studded with adherent bacteria, while lactobacilli are rod-shaped bacteria. Also, check the vaginal pH and perform a potassium hydroxide, or KOH, whiff test. To do this, smear the discharge on a slide and place a drop of 10% KOH onto the discharge while assessing for the characteristic fishy odor.

Now here is a high-yield fact! There are multiple ways to diagnose BV. Using Amsel criteria is the preferred method due to its low cost and rapid results. Three out of the four Amsel criteria must be met, including: thin, homogeneous vaginal discharge on physical exam; clue cells on microscopy; vaginal fluid pH greater than 4.5; and a positive whiff test. Next, Nugent scoring is a more reliable test for BV, but requires a gram stain of the vaginal discharge, and is primarily used in research settings. Finally, nucleic acid amplification tests, or NAATs, and polymerase chain reaction or PCR tests are also available, but are more expensive and take longer to get results.

Okay, let’s go over the results. First, the findings might be completely normal. So, if the saline microscopy demonstrates an absence of clue cells with the presence of abundant lactobacilli; the vaginal pH is less than or equal to 4.5; and the KOH whiff test is negative, consider an alternative diagnosis. On the other hand, if the saline microscopy shows the presence of more than 20% clue cells and decreased lactobacilli; the vaginal pH is greater than 4.5; and the KOH whiff test is positive, you have made your diagnosis of bacterial vaginosis.