Illness script
Bacterial Vaginosis
Reproductive-age woman with thin, gray, malodorous ('fishy') vaginal discharge and no significant inflammation.
This illness script for Bacterial Vaginosis covers the classic presentation, who it affects, how you work it up, the mechanism, and first-line treatment—written for USMLE Step 1 and clerkship clinical reasoning.
Updated Jul 18, 2026All scripts
01
Who it affects
- Reproductive-age women
- Risk: douching, new/multiple sex partners
- More common in Black women
- Associated with IUD use, smoking
- Not classically an STI but linked to sexual activity
02
Diagnostics & workup
- Amsel criteria: need 3 of 4
- Thin homogeneous gray-white discharge
- Vaginal pH >4.5
- Positive whiff test (KOH → fishy amine odor)
- Clue cells on saline wet mount (epithelial cells studded with bacteria)
- Gold standard: Nugent score (Gram stain); Little/no WBCs or itching
03
Pathophysiology
- Loss of protective H2O2-producing Lactobacilli
- Overgrowth of anaerobes: Gardnerella vaginalis, Mobiluncus, Prevotella
- Rise in vaginal pH (>4.5)
- Amine byproducts cause characteristic fishy odor
- Polymicrobial biofilm, not inflammatory infection
04
Treatment
- Metronidazole 500 mg PO BID x7 days (first-line)
- Alternative: metronidazole gel or clindamycin cream
- Avoid alcohol with metronidazole (disulfiram reaction)
- Treat symptomatic patients; treat pregnant patients (risk of preterm birth, PROM)
- Partner treatment not routinely recommended
- Recurrence common; screen/treat before gynecologic procedures
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.