Bacterial Vaginosis and Candidal Vulvovaginitis are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.
Bacterial Vaginosis vs Candidal Vulvovaginitis at a glance
Bacterial Vaginosis: Dysbiosis of vaginal flora — loss of lactobacilli with overgrowth of anaerobes; thin gray discharge with fishy odor.
Candidal Vulvovaginitis: Yeast infection of the vulva/vagina — thick white discharge, intense pruritus, normal pH.
Try two board-style questions on Bacterial Vaginosis vs Candidal Vulvovaginitis
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Question 1ReproductiveMedium
A 27-year-old woman presents with a 2-week history of a thin gray-white vaginal discharge and a fishy odor that worsens after intercourse. She reports no vulvar itching or burning. Pelvic examination reveals a homogeneous discharge coating the vaginal walls without erythema or cervical friability. Vaginal pH is 5.0. A sample of the discharge is prepared for microscopy. Which of the following findings best supports the diagnosis?
AAbundant neutrophils with intracellular gram-negative diplococci present
BEpithelial cells coated with adherent bacteria obscuring their borders
CMotile flagellated protozoa swimming actively on a saline wet mount
DBranching pseudohyphae and budding yeast on potassium hydroxide prep
Reveal answer & full explanation
Correct answer: B — Epithelial cells coated with adherent bacteria obscuring their borders
AAbundant neutrophils with intracellular gram-negative diplococci present
BEpithelial cells coated with adherent bacteria obscuring their borders✓
CMotile flagellated protozoa swimming actively on a saline wet mount
DBranching pseudohyphae and budding yeast on potassium hydroxide prep
Why Epithelial cells coated with adherent bacteria obscuring their borders is correct
These are clue cells — vaginal epithelial cells so densely coated with adherent coccobacilli that their borders become indistinct. They are the microscopic hallmark of bacterial vaginosis.
BV is diagnosed clinically by the Amsel criteria (3 of 4): thin homogeneous gray-white discharge, vaginal pH >4.5, positive whiff (amine) test with KOH, and clue cells on saline wet mount. This patient already has the discharge, an elevated pH of 5.0, and the odor, so clue cells confirm the diagnosis.
The wet mount in BV also shows few lactobacilli and an absence of WBCs, reflecting overgrowth of anaerobes without an inflammatory response.
Why the others are wrong
Branching pseudohyphae and budding yeast on potassium hydroxide prep — this is the finding in vulvovaginal candidiasis, which presents with thick white "cottage cheese" discharge, intense pruritus, vulvar erythema, and a normal pH <4.5, not the thin gray odorous discharge with pH 5.0 seen here.
Motile flagellated protozoa swimming actively on a saline wet mount — motile trichomonads indicate trichomoniasis, which causes a frothy yellow-green discharge, a strawberry cervix, and pH >4.5; the discharge here is gray-white and homogeneous without those features.
Abundant neutrophils with intracellular gram-negative diplococci present — this points to gonococcal cervicitis, which produces mucopurulent cervical discharge and friability with many WBCs; BV characteristically lacks neutrophils and cervical friability.
Question 2ReproductiveMedium
A 28-year-old woman presents with 4 days of intense vulvar itching, burning, and a thick white discharge after finishing a course of amoxicillin 1 week ago. She is not pregnant and uses condoms for contraception. On exam, the vulva is erythematous and edematous with excoriations, and adherent white plaques are noted on the vaginal walls. There is no fishy odor, and the vaginal pH is 4.0. Microscopy of the vaginal secretions is performed. Which of the following findings best supports the most likely diagnosis?
AMotile flagellated protozoa on saline wet mount
BSheets of neutrophils without visible organisms
CBudding yeast and pseudohyphae on KOH wet mount
DEpithelial clue cells seen on saline wet mount
Reveal answer & full explanation
Correct answer: C — Budding yeast and pseudohyphae on KOH wet mount
AMotile flagellated protozoa on saline wet mount
BSheets of neutrophils without visible organisms
CBudding yeast and pseudohyphae on KOH wet mount✓
DEpithelial clue cells seen on saline wet mount
Why Budding yeast and pseudohyphae on KOH wet mount is correct
The picture of recent antibiotic use, intense pruritus, vulvar erythema/edema, thick odorless white plaques, and a normal pH of 4.0 is classic for candidal vulvovaginitis.
A 10% KOH preparation lyses epithelial cells and reveals budding yeast and pseudohyphae of Candida albicans, directly confirming the suspected organism.
Normal pH (less than 4.5) plus KOH yeast/pseudohyphae is diagnostic; recurrent disease prompts a fasting glucose or A1c.
Why the others are wrong
Motile flagellated protozoa on saline wet mount — Motile trichomonads indicate trichomoniasis, which produces a frothy yellow-green discharge and a pH greater than 4.5, not the findings here.
Epithelial clue cells seen on saline wet mount — Clue cells are epithelial cells studded with bacteria and are the hallmark of bacterial vaginosis, which has a pH greater than 4.5 and a fishy odor.
Sheets of neutrophils without visible organisms — A purely inflammatory smear is nonspecific and, absent demonstrable yeast or pseudohyphae, does not support Candida over other causes of vulvovaginitis.
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Dysbiosis of vaginal flora — loss of lactobacilli with overgrowth of anaerobes; thin gray discharge with fishy odor.
Yeast infection of the vulva/vagina — thick white discharge, intense pruritus, normal pH.
Classic presentation
Reproductive-age woman with thin gray discharge, fishy odor after intercourse, vaginal pH >4.5, clue cells on wet mount, positive whiff test.; 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%…
Woman after antibiotic use with severe vulvar itching, vulvar erythema, thick curd-like discharge, normal pH, and yeast/pseudohyphae on KOH prep.; Intense vulvar and vaginal pruritus (hallmark); Burning, soreness, irritation; External dysuria (urine contacting inflamed vulva); Dyspareunia; Thick white 'cottage cheese' discharge —…
Workup / key labs
Amsel criteria (3 of 4): (1) thin homogeneous gray-white discharge, (2) vaginal pH >4.5, (3) positive whiff test with KOH, (4) clue cells on saline wet mount. Nugent score (gram-stain based) is research/lab gold standard.; Vaginal pH (normal 3.8-4.5; BV >4.5); Wet mount: clue cells (epithelial cells coated with bacteria obscuring…
Vaginal pH normal (<4.5) — important distinguishing feature; 10% KOH wet mount: budding yeast, pseudohyphae (C. albicans) or budding yeast without pseudohyphae (C. glabrata); Negative whiff test; Culture if recurrent, severe, or atypical (identifies non-albicans species and resistance); Fasting glucose or A1c if recurrent — screen for…
First-line treatment
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
Uncomplicated: fluconazole 150 mg PO × 1 dose; Topical azole alternatives × 1-7 days: clotrimazole, miconazole, terconazole, tioconazole (available OTC); Patient symptom relief usually within 24-48 hours; Prefer a topical azole when oral fluconazole poses QT-prolongation or drug-interaction risk (e.g., other QT-prolonging drugs,…
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