Bacterial Vaginosis: Clinical Diagnosis & Treatment

Clinical Features & The Amsel Diagnostic Criteria

The hallmark clinical symptom of BV is a thin, homogeneous, off-white or grey vaginal discharge accompanied by a characteristic 'fishy' odour, often most noticeable following sexual intercourse or during menses (due to alkaline semen and blood volatilising aromatic amines).

In clinical practice, bedside diagnosis relies on the Amsel Criteria (at least 3 of 4 required):

1. Thin, homogeneous, milky-grey discharge smoothly coating the vaginal walls.
2. Vaginal pH greater than 4.5 (tested using narrow-range pH paper).
3. Positive 'Whiff test' (release of a fishy amine odour upon addition of 10% potassium hydroxide [KOH] to a drop of discharge).
4. Presence of 'Clue cells' on saline wet mount microscopy (vaginal squamous epithelial cells studded with adherent coccobacilli, obscuring the distinct cell border) on >20% of epithelial cells.

Differential Diagnosis: Differentiating BV from Thrush and Trichomoniasis

Accurate clinical differentiation is crucial before prescribing:

• Vulvovaginal Candidiasis (Thrush): Typically thick, white, curdy ('cottage-cheese') discharge associated with intense vulval itching, erythema, and dyspareunia. Vaginal pH is usually normal (≤ 4.5).
• Trichomoniasis: Sexually transmitted protozoan infection characterised by a frothy, yellow-green discharge, severe vulval irritation, dysuria, and occasionally a 'strawberry cervix'. Vaginal pH is > 4.5.

First-Line Therapeutic Regimens

Treatment is indicated for symptomatic women, women undergoing gynaecological procedures (e.g. IUD insertion or surgical termination to prevent pelvic inflammatory disease), and pregnant women:

• Oral Metronidazole: 400 mg orally twice daily for 5 to 7 days. (Patients must strictly avoid alcohol consumption during and for 24 hours post-treatment due to a disulfiram-like disulfiram reaction).
• Topical Metronidazole Gel (0.75%): One applicatorful (5 g) intravaginally at bedtime for 5 consecutive nights. Offers comparable efficacy to oral therapy with fewer systemic gastrointestinal side effects.
• Topical Clindamycin Cream (2%): One applicatorful (5 g) intravaginally at bedtime for 7 consecutive nights. (Note: Clindamycin cream is oil-based and weakens latex condoms and diaphragms).

Management of Recurrent Bacterial Vaginosis

Recurrence occurs in up to 50% of women within 6 months, driven by the persistence of antimicrobial-resistant polymicrobial biofilms on the vaginal epithelial surface. Strategies for recurrent BV include:

• A secondary extended course of oral metronidazole or clindamycin, followed by long-term suppressive maintenance therapy (e.g. Metronidazole gel twice weekly for 4 to 6 months).
• Elimination of vaginal douching, bubble baths, and commercial feminine washes, preserving natural acid mantle defences.