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Trichomoniasis

SNOMED: 240600000Updated 03/03/2026

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Exam Tips

NAAT on vaginal swab is the diagnostic test of choice; wet mount is less sensitive.
Classic frothy yellow-green discharge is testable but not universal; many patients are asymptomatic.
Vaginal pH > 4.5 supports trichomoniasis or BV rather than candidiasis.
Always test for concurrent STIs (chlamydia, gonorrhoea, HIV, syphilis) in suspected or confirmed cases.
Most treatment failures in exams are due to reinfection: treat partners concurrently and advise abstinence until completion.
Remember obstetric and HIV-transmission implications when counselling.

Definition

Trichomoniasis is a sexually transmitted infection caused by the flagellated protozoan Trichomonas vaginalis, which primarily infects the lower urogenital tract (vagina/urethra in women, urethra in men). Transmission in adults is almost always via sexual contact, although vertical transmission can occur during vaginal delivery; many infections are asymptomatic, which contributes to underdiagnosis.

Pathophysiology

T. vaginalis is an extracellular, motile protozoan that adheres to urogenital epithelial cells and triggers local inflammation through direct cytotoxic effects and host immune activation. This causes vaginitis/urethritis symptoms (discharge, irritation, dysuria) and raises vaginal pH by disrupting normal lactobacillus-dominant flora, which also increases susceptibility to bacterial vaginosis and other STIs. Persistent mucosal inflammation is thought to explain links with adverse reproductive outcomes and increased HIV transmission/acquisition risk. See Figure: classic "strawberry cervix" appearance on speculum examination.

Risk Factors

Current or recent gonorrhoea or chlamydia infection (especially in women)
Two or more sexual partners in the previous year
Inconsistent condom use
Co-existing bacterial vaginosis
Higher local prevalence networks (including some black and mixed-ethnicity sexual networks in UK surveillance data)

Clinical Features

Symptoms

Often asymptomatic (approximately 10-50% overall)
Vaginal discharge (commonest female symptom; may be thin/scanty or profuse/thick)
Vulval itch, soreness, irritation, or offensive odour
Dysuria
Male urethral discharge (often small volume) and/or dysuria
Urinary frequency or urethral irritation in men

Signs

Yellow-green frothy vaginal discharge (classic but not always present)
Vulvitis or vaginitis on examination
Cervicitis with punctate haemorrhages ("strawberry cervix") in a minority
Vaginal pH greater than 4.5
Often no visible abnormality on examination
Rarely balanitis/balanoposthitis in men

Investigations

NAAT for Trichomonas vaginalis (preferred test):Positive T. vaginalis nucleic acid on vaginal swab (self-taken or clinician-taken in women) or urethral/penile-meatal swab in men

High vaginal swab microscopy/culture (where available):Motile trichomonads on wet mount or growth on culture; sensitivity lower than NAAT

Vaginal pH testing:pH > 4.5 supports trichomoniasis/BV rather than candidiasis

Speculum examination:Frothy discharge, vaginal/cervical inflammation, occasionally strawberry cervix

Full STI screen:Screen for chlamydia, gonorrhoea, HIV, and syphilis (plus hepatitis testing if high risk) due to frequent co-infection

Management

Lifestyle Modifications

Refer to or discuss with sexual health (GUM) services for confirmation, partner management, and surveillance
Abstain from sex until patient and current partner(s) have completed treatment and symptoms have resolved
Partner notification and epidemiological treatment of recent sexual partners, even if asymptomatic
Condom advice and STI risk-reduction counselling
Offer/arrange testing for other STIs at the same episode

Pharmacological Treatment

Nitroimidazole antiprotozoal

Metronidazole 400 mg orally twice daily for 5-7 days (commonly preferred regimen)
Metronidazole 2 g orally as a single dose (alternative regimen)

Treat sexual partners at the same time to reduce reinfection. Avoid alcohol during treatment and for 48 hours after metronidazole (disulfiram-like reaction risk). Check interactions (notably warfarin with INR rise, lithium, disulfiram). Use caution in severe hepatic impairment and significant neurological disease. In pregnancy, metronidazole is generally used when indicated; multi-day oral regimens are commonly preferred in specialist guidance. If breastfeeding and using high-dose single therapy, discuss temporary interruption of breastfeeding per local policy/BNF advice.

Management of persistent/recurrent infection

Repeat metronidazole regimen after excluding non-adherence and reinfection
Specialist-directed high-dose nitroimidazole regimens if resistance suspected

Recurrent disease is often reinfection rather than true resistance; confirm partner treatment and consider specialist resistance testing pathways.

Complications

Preterm birth and low birthweight
Postpartum sepsis risk
Pelvic inflammatory disease
Facilitated HIV transmission/acquisition
Altered vaginal microbiome and bacterial vaginosis susceptibility
Female infertility
Male prostatitis (acute or chronic)
Male infertility
Association with cervical cancer risk
Association with prostate cancer risk

Prognosis

Many infections are asymptomatic and may be missed without targeted testing. Untreated infection may persist, although spontaneous clearance occurs in a minority (about 20-25%); recurrence is common (roughly 5-37%), usually due to reinfection from untreated partners. With appropriate nitroimidazole therapy and partner treatment, symptom and microbiological cure rates are high.