Bacterial Vaginosis (BV)
BASHH Bacterial Vaginosis. Last updated: Dec 2012.
NICE CKS Bacterial vaginosis. Last revised: Jul 2023.
Background Information
Aetiology
BV is caused by the overgrowth of Gardnerella vaginalis and other anaerobic bacteria
Risk Factors
Seen almost exclusively in sexually active women (but technically NOT a STI):
- Vaginal douching
- Receptive cunnilingus (oral sex)
- Smoking
- Black race
- Recent change of sex partner
- Presence of an STI (e.g. chlamydia or herpes)
Clinical Features
BV is the commonest cause of abnormal discharge in women of childbearing age.
Typical symptoms:
- ~50% are asymptomatic
- Offensive fishy-smelling vaginal discharge
Signs:
- Thin, white, homogeneous discharge
- Coating the vagina and vestibule walls
BV is NOT usually associated with signs of inflammation e.g. irritation, itching, or soreness. However, this is typically seen in trichomoniasis.
Both trichomoniasis and bacterial vaginosis cause offensive fishy-smelling vaginal discharge
- Discharge in bacterial vaginosis is typically thin, white, and homogeneous
- Discharge in trichomoniasis is classically yellow-green and frothy (but could also vary in consistency)
Complications
BV is associated with several obstetric and gynaecologic complications:
- Miscarriage
- Pre-term labour and delivery
- Pre-term premature rupture of membranes
- Low birthweight baby
- Postpartum endometritis, postpartum wound infections, post-surgical infections
- Subclinical PID
Other:
- Increased risk of acquiring STIs (including HIV, chlamydia, gonorrhoea, trichomonas, HSV-2)
- Possible link between acquiring HPV and development of cervical cancer
- BV recurrence is common
Diagnosis
There are 2 main approaches recommended by BASHH (Amsel’s and Hay/Ison criteria). Also see the NICE CKS criteria.
Amsel’s Criteria
BV is diagnosed if 3 out of 4 are present:
- Thin, white, homogenous discharge
- Clue cells present (on microscopy)
- Vaginal fluid pH >4.5
- Release of fishy odour upon adding KOH (Whiff test)
Hay/Ison Criteria
The Hay/Ison criteria are used on microscopy of Gram-stained vaginal smears:
- Grade 1 (Normal flora): Lactobacillus morphotypes predominate
- Grade 2 (Intermediate): mixed flora with some Lactobacilli present, but Gardnerella or Mobiluncus morphotypes also present (Lactobacilli ≈ Gardnerella)
- Grade 3 (BV): predominantly Gardnerella and/or Mobiluncus morphotypes. Few or absent Lactobacilli (Gardnerella >> lactobacilli)
NICE CKS Criteria
Diagnosis can be made if:
- Typical clinical symptoms + no itch or soreness
- Vaginal pH >4.5
There is no need for a swab for microscopy and/or culture if the above are met (done if testing of pH cannot be performed or there is diagnostic doubt)
Points regarding taking a discharge sample:
- Roll the swab anywhere on the vaginal wall to obtain a sample
- AVOID collecting the sample from the cervix (which has alkaline secretions) and the posterior vaginal fornix (where cervical secretions can collect)
- To test the pH: rub the discharge onto a narrow-range pH paper (urine pH dipsticks are NOT suitable)
Note that a vaginal discharge pH >4.5 is suggestive of, but NOT specific to BV.
- Trichomoniasis is another recognised cause of raised vaginal pH (>4.5)
- Normal pH with vulvovaginitis is seen with vaginal candidiasis
Management
General Advice / Conservative Management
Advice to avoid the risk factors:
- Stop smoking
- Avoid vaginal douching
- Avoid the use of antiseptics / bubble baths / shampoos in the bath
Vaginal douching and bubble baths are discouraged because they disrupt the normal lactobacillus‑dominated flora and raise vaginal pH, creating an environment that allows overgrowth of BV‑associated anaerobes.
Pharmacological Management
Treatment is only indicated if symptomatic
1st line regimen (any):
- Oral metronidazole 400mg BD for 5-7 days
- If adherence to treatment is an issue → oral metronidazole 2g single dose
- If patient prefers topical treatment / cannot tolerate oral treatment → intravaginal metronidazole gel / clindamycin cream
2nd line:
- Oral clindamycin
- Oral tinidazole
Note that alcohol interacts with BOTH oral and topical metronidazole.
Management in Pregnant/Breastfeeding Individuals
Similar to treatment in non-pregnant individuals:
- Treatment is only indicated in symptomatic individuals
- 1st line: oral metronidazole 400mg BD for 5-7 days
- If prefer topical treatment / cannot tolerate oral treatment → intravaginal metronidazole gel / clindamycin cream (only 2nd/3rd trimester)
Avoid oral metronidazole 2g single dose in pregnancy/breastfeeding.
Follow Up
Test of cure is not required if symptoms resolve.
Partner Testing and Management
Routine testing and treatment of sexual partners for bacterial vaginosis is not currently recommended in standard practice
References