Bacterial vaginosis is an overgrowth of anaerobic bacteria and loss of lactobacilli (the most frequently isolated organism in the healthy human vagina).
It is the most common cause of vaginal discharge in women of childbearing age.
🦠 Pathophysiology and causative agents
Lactobacilli are the most abundant bacteria in the vagina. They are a part of the microbiota and inhibit binding of other bacteria to the epithelial cells. They produce lactic acid that kills or inhibits the other bacteria as well, but at the same time they are well tolerated by the vaginal cells themselves.
In bacterial vaginosis, lactobacilli are lost and the normal acidity of the vagina (3.5 - 4.5) is lost and the pH goes above 4.5+.
This allows other, previously inhibited, bacteria to overgrow and colonise the vagina → bacterial vaginosis.
⚠️ Risk factors
- Sexually active - it is not an STI but sexual activity or concurrent STIs increase the risk of developing BV.
- Douches, deodorants, vaginal washes
- Copper IUD
- Smoking
🍀 Protective factors
- Condom use
- Circumcised partner
- Hormonal contraception
😷 Presentation
~50% of women are asymptomatic.
Symptoms that may present are:
- Increased vaginal discharge
- Greyish-white watery discharge
- Fishy smelling - this is a characteristic smell of BV. It is more prominent after intercourse.
There is typically no itching, soreness or irritation.
On examination, we may see this discharge coating the walls of the vagina.
🔍 Investigations
Often the diagnosis of BV may be made clinically through history and confirmed with a trial of empirical antibiotics.
There is no need for examination and investigations if:
- Low risk for STI
- No other symptoms of other conditions causing discharge
- Symptoms have not developed pre- or post-gynaecological procedure
- Not postnatal or post-miscarriage
- First episode or if recurrent, previous episode of symptoms was diagnosed as BV
- Not pregnant
However, we may opt to examine and investigate if there is concern:
- Clinical examination
- Palpate abdomen for mass or tenderness (indicative of malignancy).
- Speculum examination - unless she has a low lying placenta. We may find the discharge coating the vaginal walls and vulva.
- pH testing - pH >4.5 is suggestive (but not specific for BV).
- Vaginal swab - to exclude other causes of symptoms from women of reproductive age. We also use it to look for clue cells.
- If women is at high-risk of STI, test for: chlamydia, gonorrhoea and trichomoniasis.
💯 Criteria
To diagnose BV, we use the Amstel criteria. At least 3 out of the 4 features are needed to make a diagnosis:
- Vaginal pH >4.5
- Homogenous greyish-white discharge
- Positive whiff test - adding 10% potassium hydroxide produces fishy odour.
- Clue cells present on wet mount - these are vaginal epithelial cells that appear fuzzy without sharp edges under a microscope. Clue cells change to this fuzzy look when they are coated with bacteria.
🧰 Management
- If asymptomatic and not pregnant, no treatment is required.
- Educate patient on reducing vaginal douching and reducing antiseptic use on vagina.
- 🥇 Antibiotics
- Metronidazole - 400mg BD for 5-7 days. Even in pregnancy, oral metronidazole should be used throughout (but high-dose metronidazole is discouraged).
- It is taken orally but intravaginal metronidazole gel (0.75%) may be prescribed.
- Intravaginal clindamycin cream (2%) is an alternative
If the symptoms are recurrent (>4 times a year) then consider intravaginal metronidazole gel (0.75%) prophylactically. Otherwise refer to genitourinary medicine specialist.
🚨 Complications
- Pregnancy complications
- Preterm labour
- Low birth weight
- Chorioamnionitis
- Miscarriage
- Increased risk of STIs