What are the diagnostic criteria and treatment options for bacterial vaginosis (BV)?

Bacterial Vaginosis Testing and Diagnosis

Diagnostic Criteria

Bacterial vaginosis should be diagnosed using Amsel's clinical criteria, requiring at least 3 of 4 findings: homogeneous white discharge coating vaginal walls, clue cells on microscopy, vaginal pH >4.5, and positive whiff test (fishy odor with KOH). 1

Clinical Criteria (Amsel's Criteria)

The diagnosis requires 3 of the following 4 criteria to be present: 1

• Homogeneous, white, noninflammatory discharge that smoothly coats the vaginal walls 1
• Clue cells present on microscopic examination of saline wet mount 1
• Vaginal pH greater than 4.5 (measured with narrow-range pH paper) 1
• Positive whiff test: fishy amine odor detected before or immediately after adding 10% KOH solution 1

Research demonstrates that individual Amsel criteria have varying accuracy—pH and vaginal discharge are most sensitive (97%), while clue cells have highest specificity (86%). 2 Importantly, combinations of just 2 criteria show sensitivity of 83-93% and specificity of 82-94%, performing as well as the traditional requirement of 3 criteria. 2

Alternative Diagnostic Methods

Gram stain can be used to determine the relative concentration of bacterial morphotypes characteristic of BV (Nugent scoring), which is an acceptable laboratory method. 1 A Nugent score ≥4 indicates BV, while 0-3 is considered normal. 3

Important pitfall: Culture of Gardnerella vaginalis is not recommended as a diagnostic tool because it lacks specificity—G. vaginalis can be isolated from vaginal cultures in half of normal women. 1 While G. vaginalis culture is highly sensitive (92%), its poor specificity (69%) makes it unreliable for diagnosis. 4

Clinical Presentation

• BV is the most prevalent cause of vaginal discharge and malodor. 1, 5
• Up to 50% of women meeting diagnostic criteria are asymptomatic, which is a critical consideration. 1, 5
• The condition results from replacement of normal H₂O₂-producing Lactobacillus species with high concentrations of anaerobic bacteria (Prevotella, Mobiluncus), G. vaginalis, and Mycoplasma hominis. 1, 5

Diagnostic Challenges

Laboratory testing fails to identify the cause of vaginitis in a substantial minority of women. 1, 6 Recent evidence shows that symptoms correlate poorly with microscopy-based diagnosis—discharge has only 5% specificity and malodor only 12% specificity compared to laboratory microscopy. 7 However, approximately 65-75% of women with typical BV symptoms but negative microscopy still experience symptom resolution with metronidazole treatment, suggesting that symptom-based diagnosis may have clinical utility in certain contexts. 7

Treatment Indications

Only symptomatic women require treatment, as the principal goal is to relieve vaginal symptoms and signs of infection. 1, 6

Exceptions—Treat Asymptomatic Women in These Situations:

• Before surgical abortion procedures: Treatment with metronidazole substantially reduces post-abortion pelvic inflammatory disease (PID). 1, 6
• Before hysterectomy or other invasive gynecological procedures (endometrial biopsy, hysterosalpingography, IUD placement, cesarean section, uterine curettage): BV is associated with endometritis, PID, and vaginal cuff cellulitis after these procedures. 1, 6
• High-risk pregnant women with history of preterm delivery may benefit from treatment to reduce risk of prematurity. 1, 6

Treatment Regimens

First-Line Options

• Metronidazole 500 mg orally twice daily for 7 days (95% cure rate) 6
• Metronidazole gel 0.75%, one full applicator (5g) intravaginally once daily for 5 days 6
• Clindamycin cream 2%, one full applicator (5g) intravaginally at bedtime for 7 days 6

Alternative Regimens

• Metronidazole 2g orally as a single dose (84% cure rate)—useful when compliance is a concern 6
• Clindamycin 300 mg orally twice daily for 7 days 1, 6
• Tinidazole 2g once daily for 2 days or 1g once daily for 5 days: FDA-approved with therapeutic cure rates of 22-32% (compared to 5% placebo) when requiring resolution of all 4 Amsel criteria plus Nugent score <4. 3

Critical Treatment Considerations

• Patients using metronidazole must avoid alcohol during treatment and for 24 hours afterward due to potential disulfiram-like reaction. 6
• Clindamycin cream is oil-based and might weaken latex condoms and diaphragms. 6
• Treatment of male sex partners does not prevent recurrence and is not recommended. 1, 6, 8
• Recurrence rates are high: 50-80% of women experience BV recurrence within one year of completing antibiotic treatment. 5, 9

Adjunctive Therapy

Probiotics containing Lactobacillus species as complementary therapy with antibiotics significantly improve cure rates (risk ratio 1.53,95% CI 1.19-1.97), particularly when metronidazole is combined with probiotics (OR 0.09,95% CI 0.03-0.26 for microbiological cure). 5

Common Pitfalls to Avoid

• Do not assume BV is always symptomatic—up to 50% of cases are asymptomatic. 1, 8
• Do not treat male sexual partners—this has not been shown to alter clinical course or reduce recurrence rates. 1, 6, 8
• Do not use G. vaginalis culture for diagnosis—it lacks specificity despite high sensitivity. 1, 4
• Do not unnecessarily treat asymptomatic women with indeterminate results unless they fall into high-risk categories (pre-procedure, high-risk pregnancy), as this exposes them to medication side effects without clear benefit. 6
• Do not fail to treat before invasive gynecological procedures—this increases risk of post-procedure infections. 6