Bacterial Vaginosis
Summary
Bacterial Vaginosis (BV) is the most common cause of abnormal vaginal discharge in women of reproductive age. It represents a polymicrobial dysbiosis (ecological imbalance) rather than a single infection. The protective, H₂O₂-producing Lactobacilli are replaced by an overgrowth of anaerobic bacteria (e.g., Gardnerella vaginalis, Atopobium vaginae). While not strictly a Sexually Transmitted Infection (STI), it is sexually associated. [1,2]
Clinical Pearls
The "Whiff" Test: Adding 10% Potassium Hydroxide (KOH) to a drop of vaginal discharge volatilizes amines (Putrescine/Cadaverine), releasing a pungent fishy smell. This is specific for BV.
pH is King: Healthy vaginal pH is acidic (3.5-4.5) due to Lactobacilli producing lactic acid. In BV, pH rises to >4.5. This is a quick bedside discriminator. (Thrush usually maintains normal acidic pH).
Biofilm: Gardnerella forms a tenacious biofilm on the vaginal epithelium. This protects the bacteria from antibiotics and the host immune system, explaining the high rate of recurrence (>50%).
Statistics
- Prevalence: Very common (up to 30% of women).
- Presentation: Often asymptomatic (50%). Classic symptom is a thin, grey/white discharge with a characteristic "fishy" odour.
Risk Factors
- Sexual Activity: New partner, multiple partners, WSW (Women who have Sex with Women).
- Hygiene: Vaginal douching, bubble baths (alkaline soaps).
- Demographics: Smoking, Black ethnicity.
- Protective: Combined Oral Contraceptive Pill (Estrogen promotes glycogen causing Lactobacilli growth).
Mechanism of Dysbiosis
- Loss of Defence: Decline in Lactobacillus species (especially L. crispatus). Loss of lactic acid.
- Anaerobic Overgrowth: Gardnerella vaginalis adheres to epithelium and creates a scaffold biofilm. Massive proliferation of anaerobes (Atopobium, Mobiluncus, Prevotella).
- Metabolic By-products: Bacteria produce proteolytic enzymes (sialidase) which peel cells (Clue Cells) and volatile amines (Fishy odour).
| Feature | Bacterial Vaginosis | Candidiasis (Thrush) | Trichomoniasis |
|---|---|---|---|
| Discharge | Thin, Grey/White | Thick, White, Curdy | Frothy, Yellow/Green |
| Odour | Fishy | None / Yeasty | Offensive |
| Itch | Minimal | Severe | Moderate |
| Inflammation | None | Erythema/Fissures | "Strawberry Cervix" |
| pH | > 4.5 | < 4.5 (Normal) | > 4.5 |
| Microscopy | Clue Cells | Hyphae/Spores | Motile Protozoa |
Symptoms
Signs
Clinical Criteria (Amsel)
Diagnosis requires 3 of 4:
- Thin, homogeneous discharge.
- Clue cells on microscopy (>20%).
- pH > 4.5.
- Positive Whiff test (Amine odour with KOH).
Microbiology (Gold Standard)
- Gram Stain (Hay/Ison Criteria):
- Grade 1 (Normal): Lactobacillus morphotypes predominantly.
- Grade 2 (Intermediate): Mixed flora.
- Grade 3 (BV): Few Lactobacilli, predominant Gardnerella/Mobiluncus morphotypes.
- NAAT/PCR: Available but expensive.
Management Algorithm
VAGINAL DISCHARGE
(Thin, Grey, pH >4.5, Fishy odour)
↓
SYMPTOMATIC or PREGNANT?
┌───────────┴───────────┐
NO YES
↓ ↓
NO TREATMENT TREATMENT
(Unless undergoing (See Below)
gynae procedure)
↓
FIRST LINE THERAPY
- Metronidazole 400mg PO BD x 5-7 days
- OR Metronidazole 0.75% Gel (Vaginal) x 5 days
- OR Clindamycin 2% Cream (Vaginal) x 7 days
↓
RECURRENT BV (>3/year)
- Check compliance / douching habits
- Prolonged Metronidazole Gel (Twice weekly for 4-6 months)
- Acidifying Gels (Lactic Acid)
1. Oral vs Topical
- Oral Metronidazole: High cure rate (70-80%). Side effects: Metallic taste, Nausea. Disulfiram reaction with alcohol (Avoid drinking during + 48h after).
- Topical: Avoids systemic side effects. Clindamycin cream weakens latex condoms (warn patients).
2. Partners
- Male: Treatment NOT recommended (does not prevent recurrence in the female).
- Female: Treatment recommended if symptomatic (high concordance in WSW).
3. Pregnancy
- Treatment is indicated for symptom relief.
- Screening asymptomatic pregnant women to prevent preterm birth is controversial (Cochrane says no benefit).
- Obstetric: Preterm birth (x2 risk), Late miscarriage (16-24 weeks), Postpartum endometritis.
- Gynaecological: Increased susceptibility to HIV/Herpes/Chlamydia, Post-abortion PID, Post-hysterectomy cellulitis.
- Recurrence is very common (30% at 3 months, 50% at 1 year).
- Persistence of biofilm is the likely cause.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Bacterial Vaginosis | BASHH (2012) | Amsel/Hay-Ison for diagnosis. Metronidazole first line. |
| STI Treatment | CDC (2021) | Updated protocols for recurrent BV (maintenance gel). |
Landmark Evidence
1. Hay et al (BMJ)
- Established the Gram Stain criteria and the link between abnormal flora and late miscarriage.
2. PREMEVA Trial
- Showed that screening and treating asymptomatic BV in pregnancy did NOT reduce preterm birth, changing practice to treat only symptomatic women.
What is BV?
It is not an infection you caught. It is an imbalance of the natural bacteria in the vagina. The "good" bacteria (Lactobacilli) that keep the vagina clean/acidic initiate a decline, allowing "nuisance" bacteria to overgrow.
Why does it smell?
The overgrowth of nuisance bacteria produces chemicals that have a strong smell. This is often more noticeable after your period or after sex because blood and semen neutralize the natural acid that keeps the smell away.
Is it dirty?
No. In fact, washing too much (douching) or using bubble baths can cause it by washing away the good bacteria.
How do I stop it coming back?
- Avoid soaps, shower gels, and antiseptics in the genital area. Use water and an emollient (like E45) only.
- Showers are better than baths.
- Use the antibiotic gel if prescribed for maintenance.
Primary Sources
- Sherrard J, et al. 2018 European (IUSTI/WHO) International Guideline on the Management of Vaginal Discharge. Int J STD AIDS. 2018.
- Hay PE, et al. Abnormal bacterial colonisation of the genital tract and subsequent preterm delivery and late miscarriage. BMJ. 1994.
- Bradshaw CS, et al. Current Treatment of Bacterial Vaginosis. Infect Dis Clin North Am. 2018.
Common Exam Questions
- Diagnosis: "Clue Cells?"
- Answer: Epithelial cells coated in bacteria (BV).
- Comparison: "pH of Thrush vs BV?"
- Answer: Thrush less than 4.5 (Acidic). BV >4.5 (Alkaline).
- Treatment: "Metronidazole advice?"
- Answer: Avoid alcohol (Disulfiram-like reaction).
- STI: "Do you treat the male partner?"
- Answer: No (Does not improve outcomes).
Viva Points
- Whiff Test Chemistry: KOH releases amines (cadaverine/putrescine) from the alkaline discharge.
- Biofilm: Explain why recurrence is so common. The biofilm acts like a fortress that antibiotics can't fully penetrate.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.