Bacterial Vaginosis

Overgrowth of anaerobic bacteria in the vagina

Aetiology

  • Caused by a loss of the lactobacilli ‘friendly bacteria’ in the vagina
  • Examples of anaerobic bacteria associated with bacterial vaginosis are:
    • Gardnerella vaginalis (most common)
    • Mycoplasma hominis
    • Prevotella species

Risk factors

  • Multiple sexual partners (although it is not sexually transmitted)
  • Excessive vaginal cleaning (douching, use of cleaning products and vaginal washes)
  • Recent antibiotics
  • Smoking
  • Copper coil

Pathophysiology

  • Lactobacilli are the main component of the healthy vaginal bacterial flora
  • These bacteria produce lactic acid that keeps the vaginal pH
     low (under 4.5)
  • The acidic environment prevents other bacteria from overgrowing
  • When there are reduced numbers of lactobacilli in the vagina, the pH rises
  • This more alkaline environment enables anaerobic bacteria
     to multiply

Clinical presentation

Symptoms

  • Thin, homogeneous, grayish-white vaginal discharge
  • Fishy odor, especially after intercourse or during menstruation
  • Minimal or absent itching
  • Usually no pain or dyspareunia

Signs

  • Discharge coats vaginal walls
  • Vulva usually appears normal
  • No significant inflammation (distinguishing feature)

Investigations

Amsel’s Criteria (Clinical Diagnosis)

Diagnosis requires ≥3 of the following 4:
  1. Homogeneous, thin, gray-white discharge
  1. Vaginal pH >4.5
  1. Positive whiff test (fishy odor after adding KOH)
  1. Clue cells >20% on microscopy (vaginal epithelial cells coated with bacteria)

Nugent Scoring (Gram Stain – Gold Standard)

  • Based on relative proportions of:
    • Lactobacilli
    • Gardnerella/Bacteroides
    • Mobiluncus
  • Score:
    • 0–3: Normal
    • 4–6: Intermediate
    • 7–10: BV

Molecular Tests

  • NAAT-based assays increasingly used
  • High sensitivity and specificity

Management

Indications for Treatment

  • Symptomatic women
  • Pregnant women with symptoms
  • Prior to gynecologic procedures

First-Line Therapy

  • Metronidazole 2 gram SD PO
  • Alternatives:
    • Metronidazole 500mg BID for 7 days
    • Clindamycin 300mg BID for 7 days