Dysbiosis of vaginal flora — loss of lactobacilli with overgrowth of anaerobes; thin gray discharge with fishy odor.
Also known as: BV, bacterial vaginosis, Gardnerella, vaginal dysbiosis
Overview
Polymicrobial alteration of the vaginal microbiome characterized by loss of protective Lactobacillus species and overgrowth of anaerobic bacteria including Gardnerella vaginalis, Prevotella, Atopobium vaginae, and Mobiluncus.
Epidemiology
Most common cause of vaginal discharge in reproductive-age women; prevalence ~20-30%. Higher rates in Black and Hispanic women; up to 50% in some populations.
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Disruption of acidic Lactobacillus-dominant microbiome → rise in vaginal pH → overgrowth of facultative and obligate anaerobes producing biofilms and volatile amines (putrescine, cadaverine, trimethylamine) responsible for the characteristic fishy odor. Not classically considered an STI but is sexually associated.
Clinical presentation
Symptoms
Thin, gray-white homogeneous vaginal discharge
Fishy odor, often worse after intercourse or menses
Minimal or no pruritus or inflammation (distinguishes from candidiasis/trichomoniasis)
~50% of cases are asymptomatic
Signs / physical exam
Thin gray-white discharge coating vaginal walls
Absence of significant erythema or edema
No friability
Classic findings
Reproductive-age woman with thin gray discharge, fishy odor after intercourse, vaginal pH >4.5, clue cells on wet mount, positive whiff test.
Differential diagnosis
Vulvovaginal candidiasis — Thick white 'cottage cheese' discharge, intense pruritus, vulvar erythema, normal pH (<4.5); KOH shows yeast/hyphae
Optional commercial molecular tests (BD Affirm, NuSwab) for high-throughput diagnosis
Diagnostic algorithm
Feature
BV
Candidiasis
Trichomoniasis
Discharge
Thin gray-white, homogeneous
Thick white 'cottage cheese'
Frothy yellow-green
Odor
Fishy, worse after sex/menses
None
Malodorous
Pruritus / erythema
Minimal
Marked
Moderate
Vaginal pH
>4.5
<4.5
>4.5
Wet mount
Clue cells
Hyphae/pseudohyphae (KOH)
Motile trichomonads
Whiff test
Positive
Negative
Often positive
First-line Rx
Metronidazole PO or vaginal
Fluconazole 150 mg PO × 1
Metronidazole 500 mg PO BID × 7d
Side-by-side comparison: bacterial vaginosis vs candidiasis vs trichomoniasis.
Treatment
First-line
Metronidazole 500 mg PO BID × 7 days
Metronidazole 0.75% vaginal gel 5 g intravaginally daily × 5 days
Clindamycin 2% vaginal cream 5 g intravaginally at bedtime × 7 days
Pregnancy
Treat all symptomatic pregnant women
Metronidazole 500 mg PO BID × 7 days OR metronidazole vaginal gel × 5 days
Treatment may reduce some adverse pregnancy outcomes
Screening of asymptomatic pregnant women is NOT routinely recommended
Recurrent BV (≥3 episodes/year)
Confirm diagnosis and exclude other causes
Extended initial course followed by suppressive metronidazole gel twice weekly × 4-6 months
Avoid douching, fragranced products
Second-line / adjunct
Tinidazole 2 g PO daily × 2 days or 1 g PO daily × 5 days
Clindamycin 300 mg PO BID × 7 days
Secnidazole 2 g PO × 1 dose
Complications
Increased risk of acquiring/transmitting HIV and other STIs
Increased risk of post-procedural infection (post-hysterectomy cuff cellulitis, post-abortion endometritis)
In pregnancy: associated with preterm birth, PROM, chorioamnionitis, postpartum endometritis (causal role debated)
Increased PID risk (modest)
PANCE pearls
BV is NOT classified as an STI — treatment of male partners does not reduce recurrence and is not recommended.
Counsel patients to avoid alcohol with oral metronidazole and tinidazole (disulfiram-like reaction); the strict 'no alcohol' restriction has been called into question but is still standard advice.
Asymptomatic BV does not require treatment except before invasive gynecologic procedures (hysterectomy, abortion, IUD insertion).
Clindamycin cream is oil-based and weakens latex condoms — use alternative contraception during and 5 days after treatment.
Recurrence is common (>50% within 6-12 months) — counsel about realistic expectations.
Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants.