What is the likely diagnosis, evaluation, and first‑line treatment for a woman presenting with vaginal discharge, itching, odor, or discomfort?

Vaginitis: Diagnosis and Treatment

Diagnostic Approach

Measure vaginal pH with narrow-range pH paper as your first step: pH >4.5 points to bacterial vaginosis or trichomoniasis, while pH ≤4.5 suggests vulvovaginal candidiasis. 1, 2

Point-of-Care Testing Algorithm

• Perform the whiff test by adding 10% KOH to vaginal discharge; a fishy amine odor is pathognomonic for bacterial vaginosis or trichomoniasis 1, 3
• Prepare a saline wet mount to identify clue cells (epithelial cells densely coated with bacteria) for bacterial vaginosis, or motile trichomonads for trichomoniasis 1, 2
• Prepare a 10% KOH preparation to visualize budding yeast or pseudohyphae for candidiasis 1, 2
• Examine the cervix for mucopurulent discharge, friability, or easily induced bleeding that suggests cervicitis from gonorrhea or chlamydia 3

When Microscopy Is Negative or Equivocal

• Order nucleic acid amplification testing (NAAT) for Trichomonas vaginalis because wet mount detects only 40–80% of infections 2, 3
• Obtain NAAT for Neisseria gonorrhoeae and Chlamydia trachomatis from vaginal or cervical swab when cervicitis is suspected or the patient is at risk 2, 3
• Consider Gram stain for definitive bacterial vaginosis diagnosis when Amsel criteria are borderline 2

First-Line Treatment by Diagnosis

Bacterial Vaginosis

Prescribe metronidazole 500 mg orally twice daily for 7 days—this achieves approximately 95% cure rates and is superior to single-dose regimens. 1, 2

• Instruct patients to avoid all alcohol during treatment and for 24 hours after completion to prevent disulfiram-like reactions 1
• Complete the full 7-day course even if symptoms resolve early to reduce recurrence risk 1
• Do not treat male sexual partners; partner therapy does not prevent recurrence 1, 2

Vulvovaginal Candidiasis

Use fluconazole 150 mg as a single oral dose for uncomplicated cases, achieving 55% therapeutic cure rates. 1

Alternative topical regimens include:

• Clotrimazole 1% cream 5 g intravaginally for 7–14 days 2
• Clotrimazole 100 mg vaginal tablet for 7 days or a single 500 mg dose 2
• Multi-day courses (3–7 days) are preferred for severe or complicated cases 2
• In pregnancy, use only topical azoles—never oral fluconazole 2, 4

Trichomoniasis

Prescribe metronidazole 500 mg orally twice daily for 7 days—this is the only sexually transmitted infection for which treatment recommendations vary by sex and provides superior cure rates to single-dose therapy. 1, 5

• Alternative: metronidazole 2 g orally as a single dose (88–95% cure rate), but this has higher treatment failure rates 2, 6
• Tinidazole 2 g orally as a single dose achieves 92–100% cure rates and may be used when metronidazole fails 7
• Treat sexual partners simultaneously with metronidazole 2 g single dose to prevent reinfection—this is mandatory. 1, 2

Critical Diagnostic Pitfalls

• Never diagnose based on discharge appearance alone; clinical characteristics are unreliable for distinguishing causes 3
• Do not rely solely on wet mount for trichomoniasis; NAAT is the preferred diagnostic method 1, 3
• Do not diagnose bacterial vaginosis without clue cells unless confirmed by Gram stain 3
• Recognize that approximately 50% of women with bacterial vaginosis are asymptomatic 2
• Be aware that 10–20% of women are asymptomatic carriers of Candida; do not treat asymptomatic colonization 2

Special Populations

Pregnancy

• Treat bacterial vaginosis in pregnancy with metronidazole 500 mg twice daily for 7 days due to associations with preterm birth 1, 2
• Treat trichomoniasis in pregnancy with metronidazole 2 g single dose, which is safe and reduces preterm birth risk 2
• Use only topical azoles for candidiasis in pregnancy—oral fluconazole is contraindicated 2, 4

Pre-Procedural Management

• Treat bacterial vaginosis even if asymptomatic before invasive gynecologic procedures (abortion, hysterectomy) to lower the risk of postoperative pelvic inflammatory disease and endometritis 2

Follow-Up Recommendations

• No routine follow-up is needed if symptoms completely resolve after treatment 1
• Re-evaluate patients with persistent or recurrent symptoms within 2 months, which may indicate treatment failure, reinfection, or mixed infections requiring extended therapy or alternative agents 1, 2
• Reconsider trichomoniasis if symptoms persist after treatment, as wet mount microscopy misses 30–50% of cases 1

Mixed Infections and Alternative Diagnoses

• Evaluate for mixed infections if laboratory testing fails to identify a cause, as a substantial minority of women have coexisting pathogens 1, 2
• Consider physiologic discharge (clear to white, odorless, pH <4.5, only epithelial cells and lactobacilli on microscopy) when all tests are negative 2
• Suspect mechanical, chemical, or allergic irritation (new soaps, detergents, douches, lubricants, latex condoms) when external vulvar inflammation is present with minimal discharge and no identified pathogens 2
• In postmenopausal women, consider atrophic vaginitis and treat with hormonal or nonhormonal therapies 4, 8