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The vagina is a dynamic ecosystem. Normal vaginal discharge is clear to white, odourless and of high viscosity. Normal bacterial flora is dominated by lactobacilli – an acidic environment (PH3.8-4.2) inhibits the overgrowth of bacteria. Some lactobacilli also produces H2O2, a potential microbicide.
Bacterial vaginosis (BV) is the most common cause of vaginal discharge in females of childbearing age (40%-50% of cases). Absence of clinical signs of inflammation is the basis for the term vaginosis rather than vaginitis.
Pathogenesis
Hydrogen peroxide-producing lactobacilli prevent overgrowth of anaerobes normally present in vaginal microbiota. A loss of lactobacilli causes a rise in pH and a massive overgrowth of vaginal anaerobes, which produce large amounts of proteolytic carboxylase enzymes (which break down vaginal peptides into a variety of amines that are volatile, malodorous and associated with increased vaginal transudation and squamous cell exfoliation).
A rise in pH facilitates adherence of Gardnerella vaginalis to the exfoliating epithelial cells, which leads to biofilm. This provides a scaffolding to which other species adhere. Subsequent desquamation of these epithelial cells leads to classic clue cells.
Risk factors
Sexual activity is a risk factor. BV is not classified as an STI due to lack of a single causative agent and absence of a clear disease counterpart in males. In contrast to trichomoniasis, chlamydial or gonococcal infection, there is a high rate of symptomatic recurrence of BV in the absence of sexual activity or reinfection. Condom use decreases risk.
BV is associated with increasing numbers of female sexual partners, or a female partner with symptomatic BV. Sexual transmission is an important factor. Sexually active monogamous female same-sex partnerships over six months tended to have concordant, stable vaginal microbiota (most concordant for normal microbiota).
Other risk factors include douching, a body mass index ≥25, cigarette smoking, diet (high-fibre diets have been associated with higher likelihood of a lactobacillus-dominant vaginal microbial community).
Clinical features
The condition is asymptomatic in 50% to 70% of cases. It has a vaginal discharge (off-white, thin, homogenous) with fishy smell that may be more noticeable after sexual intercourse and during menses.
Dysuria, dyspareunia, pruritis, burning or vaginal inflammation such as erythema and oedema suggest a mixed infection (more than one pathogen involved).
Treatment of symptomatic patients
The following options are available:
- Dequalinium chloride vaginal tablets– insert one tablet every evening deep into vagina for six days
- Metronidazole500mgs orally twice daily for seven days
- Metronidazole gel 0.75%(5g contains 37.5mg metronidazole once daily vaginally for five days)
- Clindamycin 2% vaginal creamonce daily at bedtime for seven days (avoid concomitant use of latex condoms)
- Oral tinidazole andsecnidazole is at a higher cost and there is less availability.
