Differentiating BV, Yeast Infection, and Trichomoniasis
Use clinical presentation, vaginal pH, and microscopy to rapidly distinguish these three infections: BV presents with thin gray discharge, fishy odor, and pH >4.5; candidiasis shows thick white discharge with pruritus and normal pH ≤4.5; trichomoniasis causes yellow-green frothy discharge with pH >4.5 and vulvar irritation.
Clinical Differentiation Algorithm
Step 1: Assess Discharge Characteristics
- BV: Thin, homogenous, gray-white discharge with fishy odor 1, 2
- Candidiasis: Thick, white, "curd-like" or "cottage cheese" discharge 1, 2, 3
- Trichomoniasis: Yellow-green, frothy, malodorous discharge 1, 4, 2
Step 2: Check Vaginal pH
- Normal pH (≤4.5): Strongly suggests candidiasis 5, 3
- Elevated pH (>4.5): Indicates BV or trichomoniasis 3, 6
Step 3: Examine Key Symptoms
- Predominant pruritus + vulvar erythema: Candidiasis 1, 5
- Fishy odor (especially after sex): BV 2
- Vulvar irritation + cervical petechiae ("strawberry cervix"): Trichomoniasis 1, 2
Step 4: Microscopy Findings
- BV: Clue cells (>20% of epithelial cells), few WBCs 3
- Candidiasis: Yeast hyphae or budding yeast (visible in 50-70% of cases) 5, 3
- Trichomoniasis: Motile flagellated protozoa (sensitivity only 60-70%) 4, 6
Critical Pitfall: Microscopy for trichomoniasis has poor sensitivity (60-70%), so negative wet mount does NOT rule out infection 4, 6. Consider NAAT testing if clinical suspicion is high.
Diagnostic Confirmation
For BV - Use Amsel Criteria (3 of 4 required):
For Candidiasis:
- KOH preparation improves visualization of hyphae 5
- Culture if microscopy negative but symptoms persist
- PCR has 90.9% sensitivity and 94.1% specificity 8
For Trichomoniasis:
- Best test: NAAT or antigen testing (most sensitive) 4, 7, 6
- Culture in Dorset medium if available 6
- Wet mount alone misses 25-40% of cases 4
Treatment Recommendations
Bacterial Vaginosis
Recommended: Metronidazole 500 mg PO twice daily × 7 days 7
Alternatives:
- Metronidazole gel 0.75% intravaginally × 5 days
- Clindamycin cream 2% intravaginally × 7 days
Partner treatment NOT needed 1
Vulvovaginal Candidiasis (Uncomplicated)
Recommended: Topical azole therapy (any of the following are equally effective) 5, 8:
- Clotrimazole 1% cream 5g intravaginally × 7-14 days
- Miconazole 2% cream 5g intravaginally × 7 days
- Fluconazole 150 mg PO single dose
For Recurrent VVC (≥3 episodes/year): Fluconazole 150 mg PO weekly × 6 months 7, 3
Partner treatment NOT needed 7
Trichomoniasis
Recommended: Metronidazole 2g PO single dose 1, 4, 9
Alternative: Metronidazole 500 mg PO twice daily × 7 days (equal efficacy ~90-95%) 4, 7
CRITICAL: Always treat sexual partners (even without testing) to prevent reinfection 1, 9. Instruct patients to avoid sex until both partners complete treatment and are asymptomatic.
Treatment failure: Re-treat with metronidazole 500 mg twice daily × 7 days; if fails again, use 2g daily × 3-5 days 4, 5
Special Considerations
Pregnancy
- BV: Clindamycin cream in first trimester; metronidazole 500 mg PO twice daily × 7 days in second/third trimester 4, 5
- Trichomoniasis: Metronidazole 2g single dose after first trimester (contraindicated in first trimester per older guidelines, but 1998 guidelines allow treatment) 5
- Candidiasis: Topical azoles only (longer courses may be needed) 7
HIV Infection
All three conditions receive identical treatment in HIV-positive patients 1, 4
Common Diagnostic Pitfalls
- Mixed infections occur: Up to 10% of cases involve multiple pathogens 10, 11. Don't stop looking after finding one organism.
- Metronidazole gel does NOT treat trichomoniasis (<50% efficacy) - only use oral formulations 4
- C. glabrata resistance: 15% of Candida infections are resistant to clotrimazole/miconazole; consider fluconazole for treatment failures 3
- Test of cure NOT needed for trichomoniasis if symptoms resolve 4, 7