What is the cause of foul-smelling vaginal discharge?

Causes of Foul-Smelling Vaginal Discharge

Bacterial vaginosis (BV) is the most common cause of foul-smelling vaginal discharge, characterized by a fishy odor and typically requires treatment with metronidazole. 1

Common Causes of Foul-Smelling Vaginal Discharge

1. Bacterial Vaginosis (Most Common)

• Clinical presentation:

  • Fishy odor (especially after intercourse or when mixed with 10% KOH)
  • Thin, homogeneous, white discharge that adheres to vaginal walls
  • Usually minimal inflammation
  • pH > 4.5
  • Presence of clue cells on microscopy 1

• Diagnostic criteria (Amsel criteria): Requires 3 of 4:

  • Homogeneous white discharge
  • Vaginal pH > 4.5
  • Positive whiff test (fishy odor with KOH)
  • Clue cells on microscopy 1, 2

2. Trichomoniasis

• Clinical presentation:
  • Profuse, yellow-green, frothy discharge
  • Malodorous discharge
  • Vaginal/vulvar irritation
  • Motile T. vaginalis visible on wet mount 1, 3
  • Often associated with inflammatory changes 2

3. Vulvovaginal Candidiasis

• Clinical presentation:
  • Typically NOT foul-smelling (important distinction)
  • Thick, white, "cottage cheese" discharge
  • Intense itching and burning
  • Vulvar erythema
  • Normal pH (≤4.5)
  • Yeast or pseudohyphae visible on KOH preparation 1, 3

Diagnostic Approach

Microscopic Examination

1. Saline wet mount:

   • Identifies motile T. vaginalis
   • Shows clue cells in BV 1

2. 10% KOH preparation:

   • Enhances visualization of yeast/pseudohyphae in candidiasis
   • Produces fishy odor in BV (whiff test) 1

3. Gram stain:

   • Nugent scoring for BV diagnosis (most accurate method)
   • Shows decreased Lactobacillus and increased Gardnerella morphotypes 1, 4

pH Testing

• pH > 4.5: Suggests BV or trichomoniasis
• pH ≤ 4.5: Consistent with candidiasis or normal flora 1, 2

Culture

• More sensitive than microscopy for T. vaginalis and Candida species
• Consider for recurrent or treatment-resistant cases 1, 2

Treatment Recommendations

For Bacterial Vaginosis

• First-line treatment:

  • Metronidazole 500 mg orally twice daily for 7 days 1

• Alternative regimens:

  • Metronidazole 2 g orally in a single dose
  • Metronidazole gel 0.75%, one applicator (5 g) intravaginally twice daily for 5 days
  • Clindamycin cream 2%, one applicator (5 g) intravaginally at bedtime for 7 days
  • Clindamycin 300 mg orally twice daily for 7 days 1

For Trichomoniasis

• Recommended regimen:

  • Metronidazole 2 g orally in a single dose 1, 3

• Alternative regimen:

  • Metronidazole 500 mg orally twice daily for 7 days 1

For Vulvovaginal Candidiasis

• Topical options: Various azole preparations (clotrimazole, miconazole, etc.) for 1-7 days
• Oral option: Fluconazole 150 mg as a single dose 1

Important Clinical Considerations

Treatment of Sexual Partners

• For BV: Not routinely recommended as it doesn't alter clinical course or recurrence rate 1
• For trichomoniasis: Treatment of partners is essential to prevent reinfection 1

Follow-up

• For BV and trichomoniasis, follow-up is unnecessary for patients who become asymptomatic 1
• Consider follow-up for persistent symptoms or recurrent infections

Special Considerations

• Pregnancy: Metronidazole 2 g as a single dose is acceptable for trichomoniasis 1
• HIV infection: Same treatment regimens as HIV-negative patients 1
• Metronidazole precautions: Advise patients to avoid alcohol during treatment and for 24 hours afterward 1

Treatment Failures

• For persistent BV or trichomoniasis despite appropriate therapy:
  • Rule out reinfection
  • Consider extended metronidazole therapy (500 mg twice daily for 7 days)
  • For recurrent trichomoniasis, consider metronidazole 2 g daily for 3-5 days 1

Prevention Strategies

• Regular genital hygiene
• Avoiding douching and irritating feminine products
• Using condoms to prevent sexually transmitted infections
• Prompt treatment of sexual partners when indicated