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Women's Health

Bacterial Vaginosis

Bacterial vaginosis is a vaginal microbiome syndrome causing thin, grey-white, fishy-smelling discharge with little inflammation; diagnosis is clinical or microscopy-supported, and current UK care prioritises symptomatic treatment, pregnancy assessment, STI exclusion and specialist management of recurrence.

In a nutshell

Bacterial vaginosis is a vaginal microbiome syndrome with thin, grey-white, fishy-smelling discharge, raised pH and little inflammation. Use symptoms, examination and Amsel or microscopy-supported diagnosis; treat symptomatic patients, follow the pregnancy and procedure pathways, exclude STIs when indicated, and refer recurrent disease rather than repeatedly prescribing antibiotics without confirmation.

Classic presentation

A person with a thin, homogeneous grey-white discharge and fishy odour, especially after sex, with a raised vaginal pH and no prominent itch or soreness.

Key points

  • BV reflects a shift from lactobacilli to mixed anaerobic flora and is not classed as an STI, although sex can trigger or pass it on.
  • Amsel diagnosis uses thin homogeneous discharge, clue cells, raised pH and a positive whiff test; at least three criteria are needed.
  • Little inflammation distinguishes BV from candidiasis and trichomoniasis, but atypical symptoms require an alternative or coexisting diagnosis assessment.
  • Treat symptomatic BV with the current oral or vaginal antimicrobial pathway; check pregnancy, breastfeeding, interactions and local policy.
  • Routine male-partner treatment is not indicated; assess symptomatic female partners and manage recurrent cases through sexual health.
  • Treat symptomatic pregnancy, but do not universally screen or treat asymptomatic pregnancy because evidence for preventing adverse outcomes is conflicting.

First-line investigation

History and examination with vaginal pH and Amsel criteria; use microscopy or a vaginal swab when the diagnosis is uncertain, recurrent, pregnancy-related, procedure-related or atypical.

Management

Exclude pregnancy, PID and STI red flags

  • Assess pain, fever, bleeding, urinary symptoms, pregnancy, procedure timing and sexual exposure before treating a discharge as uncomplicated BV.4,2

Confirm the syndrome and treat symptoms

  • Use Amsel or microscopy-supported assessment where needed and follow the current oral or vaginal antimicrobial regimen, with pregnancy, breastfeeding and interaction checks.1,3,6

Handle pregnancy and procedures carefully

  • Treat symptomatic pregnancy and follow local procedure pathways; universal screening or treatment of asymptomatic pregnancy is not supported by current evidence.4,1,3

Reduce irritant exposure and explain partner care

  • Avoid douching and fragranced vaginal products; do not routinely treat male partners, but assess women with symptoms or recurrent BV through sexual health.1,2

Confirm recurrence before specialist suppression

  • No test of cure is needed if symptoms resolve; recurrent or persistent symptoms need examination, repeat appropriate testing and sexual-health or gynaecology referral.1,2,8

Exam traps

  • BV usually causes little inflammation; marked itch, soreness, lesions, bleeding or pelvic pain suggests another or coexisting diagnosis.
  • A raised vaginal pH is supportive but not specific, and Amsel diagnosis requires at least three criteria.
  • BV is not classed as an STI, but sex can trigger or pass it on; routine treatment of male partners is not indicated.
  • Treat symptomatic BV in pregnancy, but do not claim that universal screening or treatment prevents preterm birth; the evidence is conflicting.
  • Do not give repeated empiric antibiotic courses for recurrent discharge without confirming BV and considering candidiasis, trichomoniasis, STI, PID or irritant causes.
  • Intravaginal clindamycin can weaken latex condoms and diaphragms.

Illustrations

Clue cells on microscopyA microscopy image of a vaginal smear showing clue cells, epithelial cells with a granular stippled border from adherent coccobacilli, with relatively few lactobacilli.CDC / M. Rein, Wikimedia Commons · Public domain

Key sources

  1. BASHH, UK national guideline on the management of bacterial vaginosis, 2012 (Latest dedicated BASHH UK guideline located for BV diagnosis, treatment, pregnancy, partner management and recurrence; BASHH lists it as last updated December 2012 and no replacement was located at the access date.)Published 1 Dec 2012
  2. NHS, Bacterial vaginosis (Current NHS information, page last reviewed 19 June 2026, covering symptoms, testing, treatment, recurrence, sex and pregnancy)Published 19 Jun 2026
  3. NHS Ayrshire & Arran Medicines, Bacterial vaginosis (UK local antimicrobial pathway reviewed August 2023 and updated March 2024, including oral regimen, pregnancy cautions, pH, swab and partner-management advice)
  4. NICE NG201, Antenatal care (Current NICE antenatal recommendations, last reviewed December 2024, including investigation of symptomatic vaginal discharge and consideration of oral or vaginal antibiotics for symptomatic BV in pregnancy)Published 19 Aug 2021
  5. Oxford University Hospitals, Genital culture and vaginal discharge laboratory guidance (Current NHS laboratory guidance describing clinical diagnosis of routine BV, when vaginal swabs are processed and when recurrent or atypical presentations need microbiological testing)
  6. BNF, Metronidazole (Current UK prescribing cross-check for metronidazole interactions, contraindications, pregnancy and breastfeeding advice; detailed BNF access is restricted in this environment)
  7. NHS Lothian, Bacterial vaginosis in pregnancy or breastfeeding (UK local pregnancy and breastfeeding pathway cross-check for symptomatic treatment, asymptomatic pregnancy uncertainty, partner management and clindamycin condom cautions; local policy applies)
  8. NHS Dumfries and Galloway, Bacterial vaginosis and frequent recurrences (UK local specialist pathway reviewed 2024 for confirmation of recurrent BV, sexual-health referral and specialist suppressive treatment options; not a substitute for local policy)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.