What is the diagnosis and first-line treatment for a 27-year-old woman with foul-smelling, frothy, green vaginal discharge?

Diagnosis and Treatment of Frothy Green Vaginal Discharge

Diagnosis: Trichomoniasis

This presentation is classic for trichomoniasis caused by Trichomonas vaginalis, and you should initiate empiric treatment with metronidazole 500 mg orally twice daily for 7 days while awaiting confirmatory testing. 1, 2

The combination of offensive (foul-smelling), frothy, and green discharge is pathognomonic for trichomoniasis. 1, 3 While bacterial vaginosis can also produce malodor, it typically presents with thin, gray-white discharge rather than green and frothy. 4, 1 Candidiasis produces thick, white "cottage cheese" discharge without odor. 1, 5

Diagnostic Workup

Obtain the following tests immediately:

• Vaginal pH using narrow-range pH paper: Trichomoniasis produces pH >4.5 in approximately 70% of cases. 1, 3, 6
• Saline wet mount microscopy: Look for motile trichomonads, though sensitivity is only 40-80% (50-75% in some studies). 1, 3, 6, 7
• "Whiff test": Add 10% KOH to discharge; a fishy odor supports trichomoniasis or bacterial vaginosis. 1, 3
• Nucleic acid amplification test (NAAT) for T. vaginalis: This is the gold standard with superior sensitivity compared to wet mount or culture. 1, 3, 8
• NAAT for Neisseria gonorrhoeae and Chlamydia trachomatis: Cervicitis from these pathogens can present with vaginal discharge. 1, 3

Critical Diagnostic Pitfall

Never rely solely on wet mount microscopy to rule out trichomoniasis—a negative wet mount does NOT exclude infection. 1, 3 Microscopy detects only 40-80% of infections, and NAAT should be ordered whenever clinical suspicion is high. 1, 7, 8

First-Line Treatment

Metronidazole 500 mg orally twice daily for 7 days is superior to single-dose therapy and should be your first-line regimen. 1, 2

Evidence Supporting 7-Day Regimen

A 2018 randomized controlled trial demonstrated that 7-day metronidazole resulted in significantly lower treatment failure rates compared to single-dose therapy (11% vs 19%, p<0.0001). 2 This represents the highest-quality, most recent evidence and should guide your treatment decision. 2

Alternative regimen: Metronidazole 2 g orally as a single dose can be used if adherence to multi-day therapy is a concern, but expect higher failure rates. 4, 1, 7

Partner Treatment is Mandatory

Treat the sexual partner simultaneously with metronidazole 2 g single dose to prevent reinfection—this is the most common cause of treatment failure. 1, 3, 6, 7 Trichomoniasis is sexually transmitted, and failure to treat partners results in reinfection cycles. 6, 9, 7

Additional Treatment Considerations

Concurrent Bacterial Vaginosis

The 7-day metronidazole regimen (500 mg twice daily) simultaneously treats both trichomoniasis and bacterial vaginosis if both are present. 1 This is a key advantage of the multi-day regimen. 1

Pregnancy

Pregnant women can safely receive metronidazole 2 g as a single oral dose, which reduces the risk of preterm birth. 1 Treatment during pregnancy is recommended. 1

Expected Side Effects

Counsel the patient that nausea (23%), headache (7%), and vomiting (4%) are common but generally mild. 2 Advise abstinence from alcohol during and for 24 hours after completing metronidazole to avoid disulfiram-like reactions. 7

Follow-Up

Reassess at 4 weeks post-treatment if symptoms persist. 2 Persistent symptoms typically indicate:

• Reinfection from an untreated partner (most common) 1, 6
• Metronidazole-resistant T. vaginalis (rare but emerging) 7, 8
• Misdiagnosis or concurrent infection 1

Test-of-Cure

Test-of-cure is not routinely required for asymptomatic patients who complete treatment and whose partners are treated. 7 However, if symptoms persist, repeat NAAT testing at 4 weeks. 2

Common Pitfalls to Avoid

• Do not diagnose based on discharge appearance alone—always confirm with pH, microscopy, and ideally NAAT. 1, 3
• Do not use topical clotrimazole or other azoles—these are ineffective against trichomoniasis (88.9% failure rate). 9
• Do not forget to treat the partner—this is the leading cause of treatment failure. 1, 6, 9
• Do not assume a negative wet mount rules out infection—order NAAT when clinical suspicion is high. 1, 3, 8