Trichomoniasis
Sexually transmitted protozoal infection — frothy yellow-green discharge, strawberry cervix; treat patient and partners.
Also known as: trichomoniasis, trich, Trichomonas vaginalis, TV
Overview
Sexually transmitted infection caused by the flagellated protozoan Trichomonas vaginalis, producing vulvovaginitis in women and urethritis (often asymptomatic) in men.
Epidemiology
Most common nonviral STI globally; ~2 million US cases/year. Disproportionate prevalence in Black women (~10%) and incarcerated populations. Frequently coexists with other STIs.
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Risk factors
- Multiple or new sex partners
- Inconsistent condom use
- Coexisting STIs, especially BV and HIV
- Incarceration
- IV drug use
- Lower socioeconomic status / limited healthcare access
Pathophysiology
T. vaginalis adheres to vaginal epithelium via surface adhesins and produces cytotoxins, causing epithelial inflammation, micro-ulceration, and increased risk of HIV transmission/acquisition. The organism cannot survive outside the urogenital tract.
Clinical presentation
Symptoms
- Frothy, malodorous yellow-green discharge
- Vulvar and vaginal pruritus, burning
- Dyspareunia, dysuria
- Postcoital bleeding
- ~50% of women and most men are asymptomatic
Signs / physical exam
- Frothy yellow-green discharge
- Vulvovaginal erythema
- 'Strawberry cervix' (punctate hemorrhages) — pathognomonic but seen in only ~2-5%
- Vaginal pH >4.5
Classic findings
Sexually active woman with frothy malodorous discharge, vulvar pruritus, and strawberry cervix on colposcopy or speculum exam.
Differential diagnosis
- Bacterial vaginosis — Thin gray discharge, fishy odor, clue cells; no motile organisms
- Candidal vulvovaginitis — Thick white discharge, intense pruritus, normal pH; KOH shows yeast
- Gonorrhea / chlamydia cervicitis — Mucopurulent cervical discharge; NAAT positive
- Atrophic vaginitis — Postmenopausal, dryness; thin pale mucosa
- Foreign body / retained tampon — Malodorous discharge resolving with removal
Diagnostic workup
Labs
- NAAT (nucleic acid amplification test) — preferred; high sensitivity/specificity
- Wet mount microscopy — motile, pear-shaped flagellated trichomonads (~50-70% sensitivity)
- Point-of-care antigen tests (OSOM Trichomonas, Affirm VPIII) — better than wet mount, suitable for clinical setting
- Culture (Diamond medium) — high specificity but slow
- Vaginal pH >4.5, often positive whiff test
- Test for other STIs: GC/CT, HIV, syphilis, HBV
Diagnostic algorithm
| Feature | Trichomoniasis | Notes |
|---|---|---|
| Causative organism | Trichomonas vaginalis (flagellated protozoan) | Only STI listed here that is a parasite |
| Classic discharge | Frothy yellow-green, malodorous | May also be thin and yellow |
| Exam clue | Strawberry cervix (punctate hemorrhages) | Present in only 2-5% but pathognomonic |
| Vaginal pH | >4.5 | Same as BV; differentiates from candidiasis |
| Diagnosis | NAAT preferred; wet mount fast but ~50-70% sensitive | Motile trichomonads on wet mount |
| Treatment (women) | Metronidazole 500 mg PO BID × 7 days | Replaced single 2 g dose (2021 CDC update) |
| Treatment (men) | Metronidazole 2 g PO × 1 | Tinidazole 2 g × 1 acceptable |
| Partner treatment | Yes — all partners | Expedited partner therapy where legal |
| Pregnancy | Treat with metronidazole | Avoid tinidazole |
Treatment
First-line
- Women: metronidazole 500 mg PO BID × 7 days (CDC 2021 — replaced single 2 g dose for women based on trial data showing lower recurrence with 7-day regimen)
- Men: metronidazole 2 g PO × 1 dose
- Alternative: tinidazole 2 g PO × 1 dose
Pregnancy
- Treat symptomatic infection — metronidazole 500 mg PO BID × 7 days (or 2 g × 1 dose)
- Metronidazole crosses placenta but evidence does not support teratogenicity; benefits outweigh risks
- Avoid tinidazole in pregnancy
- Counsel about preterm birth risk; treatment does not consistently reduce this risk
HIV-positive women
- Metronidazole 500 mg PO BID × 7 days (single-dose regimen less effective)
- Re-screen at 3 months
- Important to treat — increases viral shedding and transmission
Second-line / adjunct
- Treatment failure: re-treat with metronidazole 500 mg PO BID × 7 days; if persistent, tinidazole 2 g PO daily × 7 days; if still refractory, susceptibility testing and high-dose tinidazole
- Avoid alcohol during and for 24 hours after metronidazole (72 hours after tinidazole) — disulfiram-like reaction
- All current sexual partners should be treated regardless of symptoms (expedited partner therapy where legal)
- Re-test all women within 3 months due to high reinfection rate
Complications
- Increased risk of HIV transmission and acquisition
- Postpartum endometritis, post-hysterectomy cellulitis
- Pregnancy: preterm birth, premature rupture of membranes, low birth weight
- PID (less common than with GC/CT)
- Male infertility (rare; epididymitis/prostatitis)
PANCE pearls
- T. vaginalis is the only STI for which the CDC switched from a single-dose to multidose regimen for women based on superiority data.
- All sexual partners should be treated — even asymptomatic ones — to prevent reinfection.
- Wet mount is rapid but insensitive; NAAT is the diagnostic test of choice when available.
- Re-screen women at 3 months due to high reinfection rates (~17%).
- Strawberry cervix is highly suggestive but infrequent — its absence does not exclude trichomoniasis.
References
- CDC STI Guidelines 2021 — CDC Sexually Transmitted Infections Treatment Guidelines, 2021 (MMWR Recomm Rep 2021)
- Kissinger et al. 2018 — Single-dose Metronidazole vs 7-day Treatment for Trichomonas in Women (Lancet Infect Dis 2018)
- ACOG PB 215 — ACOG Practice Bulletin No. 215: Vaginitis in Nonpregnant Patients
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