01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Bacterial vaginosis is a polymicrobial shift from a lactobacillus-dominant acidic vaginal environment to anaerobic and facultative organisms, often with a Gardnerella-rich biofilm. The altered metabolism raises pH and releases volatile amines, producing the characteristic odour. Approximately half of affected people may be asymptomatic. BV is associated with sexual activity and partner change, yet its biology and management do not support treating it as a single transmissible pathogen.
Typical symptoms are thin, smooth, homogeneous white or grey discharge coating the vaginal walls and a fishy smell, often more noticeable after sex or during menstruation. Itch, marked soreness and vulval inflammation are unusual and suggest candidiasis, dermatitis, trichomoniasis or mixed disease. Pelvic pain, fever, cervical tenderness and abnormal bleeding move the assessment toward cervicitis, PID, pregnancy complication or malignancy rather than uncomplicated BV.
Diagnosis can use a Gram-stained vaginal smear graded by Hay–Ison or Nugent criteria. Amsel diagnosis requires at least three findings: homogeneous discharge, vaginal pH above 4.5, clue cells on microscopy and amine odour after alkali. Culture of Gardnerella is not useful because it can occur without BV. Molecular panels can detect associated organisms but should be used only where locally validated and interpreted against symptoms, avoiding treatment of a laboratory label alone.
Recommended treatments include metronidazole 400 mg orally twice daily for five to seven days, oral metronidazole 2 g once, intravaginal metronidazole 0.75% gel daily for five days, or intravaginal clindamycin 2% cream daily for seven days. The multidose oral course is often used because it balances effectiveness and tolerability. Check product-specific interactions, alcohol wording and barrier-contraceptive cautions rather than repeating advice from a different formulation.
Symptomatic BV in pregnancy should be treated using an accepted regimen. Current BASHH guidance does not support routine treatment of every asymptomatic pregnant person found to have BV; selected patients with additional preterm-birth risk need maternity-led assessment. Test of cure is unnecessary when symptoms resolve. Recurrence is common because the biofilm and ecological drivers may persist, so confirm the syndrome, avoid vaginal irritants, reassess sexual-health risks and distinguish relapse from candidiasis, trichomoniasis or a retained foreign body.
Key points
- Bacterial vaginosis is vaginal dysbiosis with reduced lactobacilli and anaerobic biofilm; it commonly causes thin homogeneous grey-white discharge and fishy odour with little itch or inflammation.
- Confirm with a Gram-stained vaginal smear using Hay–Ison or Nugent criteria, or with at least three of four Amsel criteria when point-of-care assessment is appropriate.
- Vaginal pH above 4.5 supports BV but is not diagnostic because semen, blood and trichomoniasis can also increase pH.
- Treat symptomatic disease with metronidazole 400 mg orally twice daily for five to seven days, metronidazole gel for five days, or clindamycin cream for seven days.
- Treat symptomatic BV during pregnancy in the usual way; do not apply routine screening or treatment to every asymptomatic pregnant person because evidence is insufficient.
- Routine partner treatment is not part of the current BASHH guideline; discuss STI testing according to exposure and avoid labelling BV as a simple classical STI.
- No test of cure is required when symptoms resolve, but recurrence is common and should be reconfirmed rather than managed with indefinite empirical repeats.
- Avoid vaginal douching, antiseptic washes and perfumed products that disrupt vaginal ecology; check intravaginal clindamycin product advice about temporary weakening of latex barriers.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Lactobacillus depletion
Loss of protective acid-producing lactobacilli raises vaginal pH and permits a dense polymicrobial community to replace the usual flora.
Anaerobic biofilm
Gardnerella-associated biofilm with other anaerobes adheres to vaginal epithelium and can persist after treatment, contributing to recurrence.
Ecological triggers
Douching, new sexual exposure, smoking, antibiotics and menstrual or hormonal changes may destabilise the microbiome without proving direct transmission.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Loss of acidity
Reduced lactic-acid production permits pH to rise above 4.5, creating conditions that favour anaerobic proliferation and inhibit protective flora.
- 2Amine production
Anaerobic metabolism generates volatile amines that produce characteristic fishy odour, especially when vaginal fluid becomes more alkaline.
- 3Clue-cell formation
Adherent coccobacilli coat epithelial borders, producing clue cells on microscopy and reflecting the attached polymicrobial biofilm.
- 4Limited inflammatory response
Unlike candidiasis or trichomoniasis, uncomplicated BV usually recruits little visible vulval inflammation despite abundant organisms and discharge.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Thin white or grey discharge that smoothly coats the vaginal walls without marked erythema is characteristic of bacterial vaginosis.
A fishy smell from volatile amines may intensify after sex or with alkali, but odour alone cannot establish the diagnosis.
Little itch, soreness or vulval erythema supports BV; pronounced inflammation should prompt testing for Candida, trichomonas or dermatosis.
Pelvic pain, fever, cervical motion tenderness or adnexal tenderness indicates possible PID and requires broader urgent treatment.
Repeated malodour after therapy can reflect true recurrent dysbiosis, incomplete treatment, retained material or a different vaginal disorder.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Gram-stained vaginal smearFirst step - Why
- Grade lactobacillus depletion and BV-associated morphotypes using Hay–Ison or Nugent criteria.
- Interpretation and limitations
- Hay–Ison grade 3 or a high Nugent score supports BV; intermediate flora requires correlation with symptoms and other findings.
- 02
Amsel clinical criteria - Why
- Diagnose BV using discharge, pH, clue cells and amine odour where microscopy is available.
- Interpretation and limitations
- At least three of four criteria support diagnosis; no single sign, including pH or odour, is sufficiently specific.
- 03
Vaginal pH - Why
- Identify loss of normal acidity and help separate BV from typical vulvovaginal candidiasis.
- Interpretation and limitations
- A value above 4.5 supports BV or trichomoniasis, while blood, semen and cervical mucus can produce false elevation.
- 04
Trichomonas and STI testing - Why
- Detect transmissible infections when exposure, inflammation, cervical discharge or pelvic symptoms raise probability.
- Interpretation and limitations
- Use validated NAAT from relevant sites; a positive result changes partner management and may require different systemic treatment.
- 05
Pregnancy and pelvic assessment - Why
- Modify treatment context and identify ectopic pregnancy, PID or maternity complications.
- Interpretation and limitations
- Treat symptomatic BV in pregnancy, but pain or bleeding requires urgent localisation and cannot be attributed to vaginal dysbiosis.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Trichomoniasis
Offensive raised-pH discharge with inflammation or a strawberry cervix suggests T. vaginalis and requires systemic partner-inclusive treatment.
Vulvovaginal candidiasis
Intense itch, erythema, fissuring, curdy discharge and usually normal pH favour Candida rather than bacterial vaginosis.
Cervicitis and PID
Mucopurulent cervical discharge, contact bleeding, pelvic pain or tenderness suggests chlamydia, gonorrhoea or upper-tract infection requiring separate care.
Retained foreign body
A retained tampon or other vaginal material can cause persistent offensive discharge, bleeding and secondary infection identified on examination.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01DIAGNOSEConfirm the dysbiosis patternFirst stepA patient presents with thin malodorous discharge and little vulval inflammation.+
- 1Ask about odour, itch, pain, bleeding, pregnancy, products, douching, antibiotics, retained material and sexual-health risks.
- 2Examine when indicated, measure vaginal pH and use Gram stain or Amsel criteria rather than relying on discharge colour alone.
- 3Test for trichomonas, chlamydia and gonorrhoea according to exposure and phenotype, adding HIV and syphilis testing where appropriate.
- 4Assess pelvic pain, pregnancy danger, ulceration or cervical lesions before classifying the condition as uncomplicated BV.
02TREATSelect oral or intravaginal therapySymptoms and validated clinical or laboratory criteria support bacterial vaginosis.+
- 1Offer metronidazole 400 mg orally twice daily for five to seven days or a guideline-listed intravaginal metronidazole or clindamycin course.
- 2Check medicines, liver and neurological history, pregnancy, breastfeeding and formulation-specific interactions or latex-barrier advice.
- 3Explain that current BASHH management does not include routine partner antibiotics and that symptoms may recur despite successful therapy.
- 4Advise avoiding vaginal douching, antiseptic or perfumed washing products and provide return advice for pelvic pain or bleeding.
03RECURReassess recurrent symptomsMalodour or discharge returns after a completed recommended regimen.+
- 1Reconfirm BV with pH, microscopy or locally validated testing instead of assuming every recurrent discharge has the same cause.
- 2Check completion, vomiting, new irritants and intravaginal product use, then examine for retained foreign material or cervical disease.
- 3Exclude candidiasis, trichomoniasis and cervicitis and assess pregnancy or upper-tract symptoms before selecting further treatment.
- 4Use a current specialist recurrence pathway for frequent proven episodes rather than indefinite unscheduled metronidazole courses.
Key medicines and prescribing safety3 treatments · regimens, roles and cautions+
Oral metronidazole
Take 400 mg orally twice daily for five to seven days for symptomatic bacterial vaginosis.Review warfarin, lithium, liver disease and neurological symptoms, and follow current product-specific advice about alcohol and breastfeeding.
Metronidazole vaginal gel
Apply 0.75% intravaginal gel once daily for five days using the supplied applicator.Confirm formulation and pregnancy suitability, explain local irritation, and do not substitute this regimen for systemic trichomoniasis treatment.
Clindamycin vaginal cream
Apply 2% intravaginal cream once daily for seven days using the product applicator.Review colitis history and diarrhoea, and warn that the cream base may weaken latex condoms or diaphragms temporarily according to product advice.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Recurrent symptoms
Persistent biofilm and repeated ecological disruption make recurrent malodour and discharge common despite initial clinical response.
Post-procedure infection
BV-associated organisms may increase infective risk around selected gynaecological procedures, which is why some procedural contexts prompt treatment.
Pregnancy association
BV is associated with adverse pregnancy outcomes, but association alone does not justify routine treatment of every asymptomatic pregnancy.
STI susceptibility
Vaginal dysbiosis correlates with acquisition of other sexually transmitted infections, supporting exposure-based screening without redefining BV as a single STI.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- No test of cure is needed when discharge and odour resolve after a completed recommended regimen.
- Reassess recurring symptoms with diagnostic criteria and exclude trichomoniasis, candidiasis, cervicitis or a retained foreign body.
- During pregnancy, coordinate any additional preterm-birth risk or obstetric symptoms with maternity care rather than applying universal screening treatment.
- Review adverse effects, interacting medicines and formulation-specific barrier-contraceptive precautions during treatment.
- Provide urgent return advice for pelvic pain, fever, heavy bleeding, pregnancy concerns or persistent cervical and vulval abnormalities.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
BV is an ecology shift
Loss of lactobacilli and anaerobic biofilm explain the raised pH, odour and tendency to recur after apparently effective treatment.
Inflammation suggests another cause
Marked itch, erythema, fissuring or pain is atypical and should prompt evaluation for candidiasis, trichomoniasis or skin disease.
Gardnerella culture misleads
The organism can be present without the syndrome, so culture does not replace validated microscopy or composite clinical criteria.
Pregnancy is symptom specific
Treat symptomatic disease, while asymptomatic screening and therapy require an obstetric risk context rather than an automatic rule.
Recurrence needs reconfirmation
Repeated empirical treatment can miss retained material, cervicitis and non-infective disease that produces similar discharge or odour.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling all fishy or grey discharge BV without microscopy or composite clinical assessment.
- 02
Using vaginal pH alone despite false elevation from semen, blood or cervical mucus.
- 03
Treating every sexual partner routinely under a guideline that does not recommend this approach.
- 04
Automatically treating every asymptomatic pregnant person with a positive laboratory pattern.
- 05
Using intravaginal metronidazole when coexisting trichomoniasis requires systemic treatment.
- 06
Repeating antibiotics indefinitely without checking retained foreign material, cervicitis or vulval disease.