Bacterial vaginosis

Overview

•Up to 50% asymptomatic - may be found incidentally

•Thin, homogeneous grey-white discharge - coats vaginal walls

•Fishy odour - worse after intercourse (alkaline semen raises pH) and during menstruation

•No significant itch or soreness - key feature distinguishing BV from candidiasis and trichomoniasis

•Normal cervix - no erythema, no cervical excitation, no strawberry cervix (strawberry cervix = Trichomonas)

Aetiology

•Polymicrobial overgrowth of anaerobes; primary organism is Gardnerella vaginalis - forms biofilm on vaginal epithelium facilitating colonisation by other anaerobes (Prevotella, Mobiluncus, Mycoplasma hominis)

•Mechanism: decline in lactobacilli → loss of lactic acid → pH rises above 4.5 → anaerobic overgrowth → volatile amines (fishy odour)

Investigations

Diagnosis is clinical using Amsel's criteria - 3 of 4 must be met:

•Thin, homogeneous grey-white vaginal discharge

•Vaginal pH > 4.5

•Positive whiff test - fishy odour on adding 10% KOH to discharge

•Clue cells on microscopy - vaginal epithelial cells densely coated with *Gardnerella*, giving stippled/'salt and pepper' appearance with obscured cell borders

🎯

Clue cells are the single most specific finding for BV on microscopy. Strawberry cervix is associated with Trichomonas vaginalis, not BV.

Differential diagnosis

Vaginal discharge differentials

Feature	BV	Candidiasis	Trichomonas
Organism	Gardnerella vaginalis (anaerobes)	Candida albicans	Trichomonas vaginalis
Discharge	Thin, grey-white, homogeneous	Thick, white, 'cottage cheese'	Frothy, yellow-green
Odour	Fishy	None	Offensive
Itch	Absent	Prominent	May be present
Vaginal pH	> 4.5	< 4.5	> 4.5
Cervix	Normal	Normal	Strawberry cervix
Treatment	Metronidazole	Fluconazole / clotrimazole	Metronidazole

Management

•Asymptomatic BV in non-pregnant women does not usually require treatment

🥇 First-line

•metronidazole oral 400 mg twice daily for 5-7 days - for symptomatic women and all pregnant women with BV

•Alternative: metronidazole intravaginal gel 0.75% once daily for 5 days - similar efficacy, fewer systemic side effects

🥈 Second-line

•clindamycin intravaginal cream 2% once nightly for 7 days - if metronidazole not tolerated; contraindicated in first trimester

•Recurrent BV (≥3 episodes in 12 months): extended suppressive therapy with intravaginal metronidazole gel twice weekly for 4-6 months after initial treatment course

•Partner treatment not routinely recommended - BV is not classified as a conventional STI

⚠️

Avoid alcohol during oral metronidazole and for 48 hours after completion - disulfiram-like reaction. Advise stopping douching and scented intimate products.

📌

In pregnancy: routine screening is not recommended in asymptomatic women. If found, oral metronidazole remains first-line. Intravaginal clindamycin cream is contraindicated in the first trimester.