Bacterial Vaginosis and Trichomoniasis

Overview

BV = DYSBIOSIS (ecosystem disruption, not single pathogen). NOT classified as conventional STI — no routine partner Rx. Trichomoniasis = genuine STI (parasitic). Partner Rx REQUIRED.

Bacterial Vaginosis

Pathogenesis: Healthy vagina = lactobacillus-dominant (lactic acid+H2O2, protective low/acidic pH). BV = lactobacillus flora DISRUPTED → anaerobic overgrowth (Gardnerella vaginalis chief, + Mobiluncus, Prevotella, Atopobium vaginae). Ecological imbalance, NO single designated causative agent (unlike conventional infection).

Clinical: thin greyish-white homogeneous discharge, FISHY ODOR (worse post-intercourse/menstruation — raises pH, volatilizes amines). Itching/inflammation NOT prominent (unlike candidiasis/trichomoniasis — useful discriminator). Significance: ↑PID risk, ↑preterm labor/low birth weight, ↑HIV/other STI acquisition susceptibility (disrupted less-acidic environment = weakened barrier).

Diagnosis: AMSEL’S CRITERIA (≥3 of 4):

1. Thin homogeneous discharge
2. Vaginal pH >4.5
3. Positive WHIFF TEST (fishy odor + 10% KOH)
4. CLUE CELLS (saline wet mount — epithelial cells studded with bacteria, obscured borders)

Nugent scoring: Gram-stain morphotype system, research/reference standard, more objective, less practical bedside.

Treatment: Metronidazole (oral/intravaginal gel) or Clindamycin (oral/intravaginal cream) = 1st line. NO routine partner treatment (dysbiosis, not STI).

Trichomoniasis

Organism: Trichomonas vaginalis. Flagellated protozoan, pear-shaped, ACTIVELY MOTILE (visible swimming on fresh wet mount). ONLY trophozoite form, NO CYST STAGE (distinctive vs most protozoa). Sexually transmitted essentially exclusively. MOST COMMON curable non-viral STI worldwide (case burden).

Clinical: Women: profuse, FROTHY, yellow-green, malodorous discharge, vulvovaginal itching/irritation, dysuria. “STRAWBERRY CERVIX” (punctate hemorrhages, minority, distinctive when present). Substantial proportion ASYMPTOMATIC/mild — diagnostic trap. Men: usually asymptomatic/mild urethritis — significant under-recognized transmission reservoir (same pattern as other STIs).

Diagnosis: Wet mount microscopy — FRESH specimen critical (motility lost quickly on cooling/drying → false negative if delayed). Fast, cheap, specific if positive, but LOWER sensitivity than newer methods. NAAT: HIGHER sensitivity, preferred where available, catches mild/asymptomatic cases wet mount misses. Culture (Diamond’s medium): more sensitive than wet mount, slower, used if NAAT unavailable.

Treatment: Metronidazole or Tinidazole (oral, single-dose/short course) = DOC. PARTNER TREATMENT ESSENTIAL regardless of symptoms (genuine STI). AVOID ALCOHOL during + defined period after (disulfiram-like reaction).

Two Causes of Vaginal Discharge, Different Mechanisms

Bacterial vaginosis and trichomoniasis are both leading causes of abnormal vaginal discharge, but they differ fundamentally in kind — bacterial vaginosis is a dysbiosis (a disruption of the normal vaginal microbial ecosystem, not an infection by any single invading pathogen), while trichomoniasis is a genuine sexually transmitted parasitic infection. This distinction matters directly for management, since BV is not classified as an STI in the conventional sense (though sexual activity is a recognized risk factor) and partner treatment is not routinely recommended for it, whereas trichomoniasis is unambiguously an STI requiring partner treatment as a matter of course.

Bacterial Vaginosis

Pathogenesis

The healthy vagina is dominated by lactobacilli, which maintain a protective, low (acidic) vaginal pH by producing lactic acid and hydrogen peroxide — a genuinely important ecological/chemical barrier against overgrowth by other organisms. Bacterial vaginosis develops when this lactobacillus-dominant flora is disrupted and replaced by an overgrowth of predominantly anaerobic organisms — chiefly Gardnerella vaginalis, alongside Mobiluncus, Prevotella, and Atopobium vaginae — a shift best understood as an ecological imbalance (dysbiosis) rather than the invasion of any single new pathogen, which is exactly why no single organism is designated “the” causative agent of BV the way it would be for a conventional infection.

Clinical Manifestations

A thin, greyish-white, homogeneous vaginal discharge with a characteristic fishy odour (notably more pronounced after unprotected intercourse or menstruation, both of which raise vaginal pH and volatilize the amine compounds responsible for the smell) — genuinely distinctive enough that odour is itself one of the standard diagnostic criteria (below). Itching and inflammation are notably not prominent features of BV, unlike candidiasis or trichomoniasis, which is a useful clinical discriminator when working through vaginal-discharge differentials. BV is clinically significant beyond simple discomfort: it is associated with an increased risk of pelvic inflammatory disease, preterm labour/low birth weight in pregnancy, and increased susceptibility to acquiring other STIs including HIV, reflecting how the disrupted, less-acidic, less lactobacillus-protected vaginal environment weakens a genuine biological barrier.

Laboratory Diagnosis

Amsel’s clinical criteria remain the standard bedside diagnostic approach, requiring at least 3 of 4 findings: (1) thin, homogeneous discharge; (2) vaginal pH >4.5 (reflecting loss of the lactobacillus-maintained acidic environment); (3) a positive “whiff test” (a fishy amine odour released on adding 10% KOH to a discharge sample, from volatilization of amines produced by the anaerobic overgrowth); and (4) clue cells on saline wet mount — vaginal epithelial cells so densely studded with adherent bacteria that their normal sharp cell-border outline is obscured/stippled, a genuinely distinctive microscopic finding. Nugent scoring (a standardized, Gram-stain-based bacterial morphotype scoring system) is the laboratory research/reference-standard alternative to Amsel’s criteria, more objective but less practical for routine bedside use.

Treatment

Metronidazole (oral or intravaginal gel) or clindamycin (oral or intravaginal cream) are both effective first-line options. Routine partner treatment is not recommended, reflecting BV’s status as a dysbiosis rather than a conventional sexually transmitted infection.

Trichomoniasis

The Organism

Trichomonas vaginalis is a flagellated protozoan parasite — pear-shaped, actively motile (visible directly swimming under the microscope on a fresh wet mount, which is exactly what makes wet-mount microscopy such a fast, satisfying bedside diagnostic tool when positive) — and exists only as a trophozoite, with no cyst stage at all, a genuinely distinctive feature among the medically important protozoa, most of which cycle between trophozoite and cyst forms. It is transmitted essentially exclusively by sexual contact, and, unlike most other protozoan infections, is the most common curable non-viral STI worldwide by case burden.

Clinical Manifestations

In women: a classically described profuse, frothy, yellow-green, malodorous discharge, with vulvovaginal itching/irritation, dysuria, and, on speculum examination, a “strawberry cervix” (punctate cervical haemorrhages from the organism’s local inflammatory effect, visible in a minority but genuinely distinctive when present) — though a substantial proportion of infected women are asymptomatic or only mildly symptomatic, another real diagnostic trap.

In men: usually asymptomatic or mildly symptomatic (mild urethritis), which is exactly why men serve as a significant, under-recognized transmission reservoir — the same asymptomatic-male pattern that complicates control of several other STIs covered in this section.

Laboratory Diagnosis

Wet mount microscopy of vaginal/urethral secretions, examined promptly while still fresh (motility is lost quickly once the specimen cools or dries, which is why delayed examination gives false negatives), directly visualizes the motile, flagellated trophozoite — a genuinely fast, low-cost, and specific test when positive, though sensitivity is meaningfully lower than more modern methods. NAAT now offers substantially higher sensitivity and is increasingly the preferred method where available, particularly useful for the milder or asymptomatic cases that wet-mount microscopy is most likely to miss. Culture (Diamond’s medium) is more sensitive than wet mount but slower, used mainly where NAAT is unavailable.

Treatment

Metronidazole or tinidazole (oral, single-dose or short course) is the treatment of choice — genuinely notable in that, unlike bacterial vaginosis, partner treatment is essential here regardless of symptoms, reflecting trichomoniasis’s status as an unambiguous STI, and both partners should also avoid alcohol during metronidazole/tinidazole treatment and for a defined period afterward, given the drug’s disulfiram-like interaction with alcohol.

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