AKT · Sexual health/Vaginitis / discharge

Bacterial vaginosis

Polymicrobial — Gardnerella vaginalis overgrowth (loss of lactobacilli)

Overview

Overgrowth of anaerobes replacing lactobacilli, raising vaginal pH. The commonest cause of abnormal discharge; not strictly an STI but linked to sexual activity. Important in pregnancy (preterm birth).

Recognise

Thin, grey-white, homogeneous discharge with a fishy odour
NON-itchy, non-inflammatory (no soreness) — unlike candida/trichomonas
Worse after sex/menses

Red flags

Pregnancy (preterm birth, late miscarriage association)

Differentials & how to tell them apart

Trichomoniasisfrothy yellow-green discharge, itch/soreness, strawberry cervix, pH also raised — but motile trichomonads on wet mount

Candidiasisthick white "cottage cheese", itchy, NORMAL pH (<4.5)

Physiological dischargeno odour, normal pH

Investigations

Raised vaginal pH >4.5; clue cells on microscopy; positive whiff test (amine odour with KOH); Hay/Ison or Amsel criteria.

Management

Metronidazole 400 mg BD orally for 5–7 days

1Symptomatic: metronidazole 400 mg BD orally for 5–7 days (or 2 g single dose).Gate: If topical preferred/oral not tolerated → intravaginal metronidazole 0.75% gel OD ×5d or clindamycin 2% cream ×7d
2Pregnancy: oral metronidazole (avoid the 2 g single dose); treat symptomatic women.
3Asymptomatic: usually no treatment unless before a gynae procedure or in pregnancy with risk.

Metronidazole — first-line; oral 400 mg BD ×5–7d (avoid alcohol)

Intravaginal metronidazole gel / clindamycin cream — topical alternative

Key points

Counsel to avoid douching/soaps. Warn re disulfiram-like reaction with alcohol + metronidazole. No TOC if symptoms resolve.

Monitor & prognosis

Symptom resolution; recurrence common.

Benign but recurrent; pregnancy implications.

Source: NICE CKS Bacterial vaginosis (2025); BASHH