Vaginal Discharge & Vaginal Infections

Vaginal discharge is one of the commonest gynaecological complaints, and three infections account for the overwhelming majority of pathological discharge: bacterial vaginosis (BV), vulvovaginal candidiasis (VVC), and trichomoniasis. For NEET PG, the single most repeated theme is differentiating these three by pH, microscopy, whiff test, and drug of choice — high-yield, near-guaranteed recall.

Physiological (normal) vaginal discharge

Before labelling discharge as infective, recognise the normal. Physiological discharge is white/clear, odourless, non-irritant, and varies with the menstrual cycle (clear and stretchy at ovulation due to oestrogen, thicker post-ovulation due to progesterone).

The healthy vaginal ecosystem is dominated by Lactobacillus (Döderlein bacilli), which metabolise glycogen (laid down under oestrogen) into lactic acid, keeping the vaginal pH between 3.8 and 4.5 (acidic). They also produce hydrogen peroxide, suppressing pathogens. Anything that disturbs this lactobacillus dominance predisposes to infection.

High-yield: Normal vaginal pH = 3.8–4.5 (acidic), maintained by lactobacilli converting glycogen → lactic acid. A pH > 4.5 is the screening clue that shifts you away from candidiasis (which keeps pH normal) towards BV or trichomoniasis.

The three core infections — overview

Feature	Bacterial vaginosis	Vulvovaginal candidiasis	Trichomoniasis
Organism	Gardnerella vaginalis + anaerobes (polymicrobial); loss of lactobacilli	Candida albicans (~90%)	Trichomonas vaginalis (flagellated protozoan)
Discharge	Thin, grey-white, homogeneous, adherent, fishy	Thick, curdy/cottage-cheese, white, non-offensive	Frothy, greenish-yellow, profuse, offensive
Odour	Fishy (amine)	Nil	Foul/offensive
Pruritus	Minimal	Intense itching, soreness	Itching + soreness
Vaginal pH	> 4.5 (often 5–6)	Normal (< 4.5)	> 4.5 (often > 5)
Whiff/amine test	Positive	Negative	May be positive
Microscopy	Clue cells	Pseudohyphae / budding yeast	Motile trichomonads, many WBCs
Inflammation	Absent (not inflammatory)	Present (vulvar erythema)	Present (strawberry cervix)
STI?	No (not classed as STI)	No	Yes (sexually transmitted)
Treatment	Metronidazole	Fluconazole / clotrimazole	Metronidazole (treat partner)

High-yield: Of the three, only candidiasis keeps the pH normal/acidic. Both BV and trichomoniasis raise the pH above 4.5. This is the fastest discriminator.

Bacterial vaginosis (BV)

Concept & pathophysiology

BV is not an infection by a single organism but a dysbiosis — a shift from a lactobacillus-dominant flora to an overgrowth of anaerobes: Gardnerella vaginalis, Mobiluncus, Prevotella, Atopobium vaginae, and Mycoplasma hominis. Loss of H₂O₂-producing lactobacilli raises the pH; anaerobic amines (putrescine, cadaverine, trimethylamine) cause the fishy odour, intensified when alkalinised by KOH or semen.

Risk factors: douching, new/multiple partners, smoking, copper IUCD. It is the commonest cause of abnormal vaginal discharge in women of reproductive age.

Amsel criteria (clinical diagnosis)

Diagnosis requires any 3 of the following 4 (Amsel criteria):

1. Thin, homogeneous grey-white adherent discharge
2. Vaginal pH > 4.5
3. Positive whiff/amine test (fishy odour on adding 10% KOH)
4. Clue cells on saline wet mount (> 20% of epithelial cells)

High-yield — Amsel criteria mnemonic: Think "Clue, pH, Whiff, Discharge" — need 3 of 4. Clue cells = vaginal epithelial cells studded with coccobacilli, giving a stippled, ill-defined ("ground-glass") border.

Gold standard & scoring

• Gram stain with Nugent score (0–10) is the laboratory gold standard: ≥ 7 = BV, 4–6 = intermediate, 0–3 = normal. It quantifies lactobacilli vs Gardnerella/Mobiluncus morphotypes.
• BV is characteristically non-inflammatory — few WBCs on microscopy (helps distinguish from trichomoniasis, which has many WBCs).

Treatment

Metronidazole 400–500 mg PO BD × 7 days (first line), or metronidazole gel, or clindamycin. Single 2 g dose is less effective for BV than for trichomoniasis.

High-yield: Routine partner treatment is NOT recommended in BV (unlike trichomoniasis). Counsel to avoid alcohol during metronidazole and for 48 h after (disulfiram-like reaction).

Why BV matters in obstetrics

BV in pregnancy is associated with preterm labour, PROM, chorioamnionitis, late miscarriage, and post-partum endometritis. Symptomatic pregnant women should be treated (oral metronidazole is acceptable in pregnancy).

Vulvovaginal candidiasis (VVC)

Organism & risk factors

~90% due to Candida albicans (germ-tube positive); the rest C. glabrata/C. tropicalis (more in recurrent/resistant disease). Predisposing factors — the classic "host with raised glycogen/immunosuppression":

• Pregnancy and diabetes mellitus (glycosuria, high glycogen)
• Recent broad-spectrum antibiotics (kill lactobacilli)
• Oral contraceptives / oestrogen, corticosteroids
• Immunosuppression / HIV, tight synthetic clothing

High-yield: Recurrent candidiasis (≥ 4 symptomatic episodes/year) should prompt screening for diabetes mellitus and HIV.

Clinical features

Intense vulvar pruritus is the hallmark, with soreness, dyspareunia, external dysuria, and thick, white, curdy/cottage-cheese non-offensive discharge. Examination: vulvar erythema, oedema, satellite lesions, adherent white plaques on the vaginal wall. pH remains normal (< 4.5).

Diagnosis

• Saline + 10% KOH wet mount: budding yeasts and pseudohyphae (KOH dissolves epithelial cells, highlighting fungal elements).
• Gram stain: gram-positive budding yeast.
• Culture (Sabouraud dextrose agar) reserved for recurrent/resistant/atypical cases.

Treatment

• Uncomplicated: single-dose fluconazole 150 mg PO, OR topical azole (clotrimazole, miconazole) intravaginally.
• Pregnancy: topical clotrimazole preferred; oral fluconazole avoided (teratogenic in higher/repeated doses).
• Recurrent VVC: induction then maintenance fluconazole 150 mg weekly × 6 months.

High-yield: In pregnancy → topical azole, NOT oral fluconazole. Candidiasis is not classed as an STI; partner treatment only if symptomatic balanitis.

Trichomoniasis

Organism & transmission

Trichomonas vaginalis is a flagellated, motile protozoan (4 anterior flagella + undulating membrane). It is a sexually transmitted infection, so screen for and treat coexisting STIs and always treat the partner. Incubation 4–28 days.

Clinical features

Profuse, frothy, greenish-yellow, offensive discharge with vulvovaginal itching and soreness, dyspareunia, and dysuria. The classic sign is the "strawberry cervix" (colpitis macularis) — punctate haemorrhagic cervical spots, seen in a minority but highly specific. pH is high (> 4.5, often > 5).

Diagnosis

• Saline wet mount: motile, pear-shaped trichomonads with jerky motility + abundant WBCs (most common, immediate test).
• NAAT is the most sensitive test (gold standard for detection).
• May be an incidental finding on Pap smear.

Treatment

Metronidazole 2 g PO single dose, OR 400–500 mg BD × 7 days. Tinidazole is an alternative. Treat the sexual partner simultaneously and advise abstinence until both are treated. Avoid alcohol (disulfiram-like reaction).

High-yield: Trichomoniasis in pregnancy → associated with preterm birth and low birth weight; metronidazole may be used. T. vaginalis infection also facilitates HIV transmission.

Stepwise clinical approach to vaginal discharge

A practical flow for the exam vignette:

History (itch? odour? colour? partner symptoms?) → Speculum exam (note discharge character, strawberry cervix, vulvar erythema) → Measure vaginal pH with litmus paper → Whiff test with 10% KOH → Microscopy: saline wet mount + KOH mount → Assign diagnosis & treat (± partner).

Decision shortcut:

1. pH normal + itch + curdy discharge + pseudohyphae → Candidiasis → fluconazole/clotrimazole.
2. pH > 4.5 + fishy odour + clue cells + whiff positive + no inflammation → BV → metronidazole.
3. pH > 4.5 + frothy green discharge + motile flagellates + strawberry cervix → Trichomoniasis → metronidazole + treat partner.

The KOH "whiff" / amine test

Add a drop of 10% potassium hydroxide to the discharge on a slide. A fishy/amine odour = positive test, indicating volatile amines from anaerobic metabolism. Positive in BV and sometimes trichomoniasis; negative in candidiasis. KOH also lyses epithelial cells and WBCs, so the same KOH mount best reveals candidal pseudohyphae.

Other / less common causes

Cause	Key clue
Atrophic vaginitis	Post-menopausal; thin, dry, sometimes blood-tinged discharge; low oestrogen; treat with topical oestrogen
Desquamative inflammatory vaginitis	Purulent discharge, high pH, no clue cells/yeast; treat with topical clindamycin/steroid
Foreign body (retained tampon, pessary)	Foul, often bloodstained discharge; commonest cause in children = foreign body/threadworm
Cervicitis (gonorrhoea/chlamydia)	Mucopurulent cervical discharge, contact bleeding — consider in STI context
Physiological leucorrhoea	Cyclical, clear/white, asymptomatic

High-yield: In a pre-pubertal girl with vaginal discharge, think foreign body, threadworm (Enterobius), or sexual abuse — not the adult triad. In post-menopausal women, think atrophic vaginitis (and exclude malignancy if blood-stained).

Complications

• BV: preterm labour, PROM, chorioamnionitis, PID, post-abortal/post-partum endometritis, increased HIV/STI acquisition, post-hysterectomy vaginal cuff cellulitis.
• VVC: local excoriation, recurrent disease, rarely systemic in immunocompromised; signals undiagnosed diabetes/HIV.
• Trichomoniasis: PID (less common), preterm birth, low birth weight, increased HIV transmission, infertility (rare).

Key differentials at a glance (microscopy is king)

Microscopy finding	Diagnosis
Clue cells (epithelial cells coated with bacteria, stippled border)	Bacterial vaginosis
Pseudohyphae + budding yeast (on KOH)	Candidiasis
Motile pear-shaped flagellates + many WBCs	Trichomoniasis
Many WBCs, no organism, mucopurulent	Cervicitis (chlamydia/gonorrhoea)
Parabasal cells, few lactobacilli	Atrophic vaginitis

Recently asked / exam angle

• Direct image/description recall: "Clue cells on wet mount" → BV; "strawberry cervix + frothy discharge" → trichomoniasis; "cottage-cheese discharge + pseudohyphae" → candidiasis. These are the most repeated single-best-answer stems.
• Amsel criteria: "How many of 4 needed?" → 3 of 4. Be able to list all four.
• pH discriminator: "Which infection has normal vaginal pH?" → Candidiasis.
• Drug of choice matching: BV/trichomoniasis → metronidazole; candidiasis → fluconazole/clotrimazole.
• Partner treatment: required in trichomoniasis, NOT routinely in BV/candidiasis.
• Pregnancy: candidiasis → topical clotrimazole (avoid oral fluconazole); BV in pregnancy → preterm labour association.
• Gold standard for BV → Nugent score (Gram stain), cut-off ≥ 7.
• Recurrent candidiasis → work up for diabetes / HIV.
• Lactobacillus / Döderlein bacilli and the glycogen → lactic acid mechanism maintaining acidic pH is a recurrent physiology one-liner.

Rapid revision

• Normal vaginal pH 3.8–4.5; maintained by lactobacilli (Döderlein) converting glycogen → lactic acid.
• BV = clue cells + fishy odour + pH > 4.5 + positive whiff → diagnose by 3 of 4 Amsel criteria; gold standard Nugent ≥ 7.
• BV is non-inflammatory (few WBCs) and is not an STI; commonest cause of abnormal discharge in reproductive-age women.
• Candidiasis = intense itch + curdy white discharge + pseudohyphae + normal pH; only infection with normal pH.
• Trichomoniasis = frothy greenish offensive discharge + strawberry cervix + motile flagellates + pH > 4.5; it is an STI → treat partner.
• Metronidazole treats both BV and trichomoniasis; avoid alcohol (disulfiram-like reaction).
• Fluconazole 150 mg single dose (or topical azole) for candidiasis; in pregnancy use topical clotrimazole, not oral fluconazole.
• Whiff test = 10% KOH → fishy amine odour; positive in BV (± trichomoniasis), negative in candidiasis.
• Recurrent candidiasis (≥ 4/year) → screen for diabetes and HIV.
• BV and trichomoniasis in pregnancy → preterm labour / low birth weight; trichomoniasis facilitates HIV transmission.
• Pre-pubertal girl discharge → think foreign body / threadworm / abuse; post-menopausal → atrophic vaginitis.
• Microscopy mantra: clue cells = BV, pseudohyphae = Candida, motile trichomonads + WBCs = Trichomonas.