Reproductive · PANCE / PANRE

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

Trichomoniasis at-a-glance: presentation, diagnosis, treatment.

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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