Trichomoniasis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Trichomonas vaginalis is a flagellated protozoan that infects squamous epithelium of the genital tract. Vaginal infection may cause profuse yellow-green or frothy discharge, vulval irritation, dysuria, dyspareunia and punctate cervical haemorrhages, but none of these findings is sufficiently sensitive or specific to establish the diagnosis. Penile urethral infection is commonly asymptomatic and can present as non-gonococcal urethritis, maintaining transmission despite an apparently well partner.

Diagnosis relies on demonstration of the organism. A validated nucleic-acid amplification test from a vaginal swab or another locally approved specimen is more sensitive than wet-mount microscopy. Wet microscopy can show motile trichomonads when examined promptly, but organism motility and sensitivity fall rapidly after collection. Culture is slower and may assist where molecular testing is unavailable. A vaginal pH above 4.5 supports trichomoniasis or bacterial vaginosis but cannot distinguish them.

Oral systemic therapy is required because topical preparations do not eradicate infection at all urogenital sites. BASHH recommends metronidazole 400 to 500 mg twice daily for seven days, with the multidose regimen producing better cure than a 2 g single dose. Metronidazole can be used throughout pregnancy and while breastfeeding; the expected benefit of treating symptomatic infection outweighs concern, while high-dose regimens should be avoided in pregnancy when an effective multidose course is suitable.

Partner treatment is inseparable from index care. Current partners should receive treatment and screening for other STIs without waiting for symptoms, because silent carriage is common. Patient and partners should avoid sexual contact for at least one week and until everyone has completed treatment and the planned follow-up. Condom advice, sexual-health testing and an agreed notification method reduce reinfection without assigning blame or inferring behaviour from anatomy.

Routine test of cure is not required after symptom resolution and completed concurrent partner care. Persistent symptoms should prompt confirmation of the original diagnosis, adherence, vomiting, re-exposure, partner treatment and the timing and type of repeat assay. NAAT too soon after therapy may detect residual nucleic acid. Confirmed persistence without reinfection requires specialist management because higher-dose metronidazole or tinidazole decisions depend on pregnancy, interactions, tolerability and possible resistance.

Key points

Trichomonas vaginalis is a sexually transmitted protozoan infection; many people are asymptomatic, while vaginitis can produce offensive yellow-green discharge, soreness, dysuria and a raised vaginal pH.
Use a validated NAAT when available because symptoms and wet-mount microscopy lack sensitivity; a negative wet mount does not exclude infection.
Give oral metronidazole 400–500 mg twice daily for seven days; the multidose course is more effective than a single 2 g dose and topical metronidazole is inadequate.
Metronidazole can be used at all stages of pregnancy and during breastfeeding under BASHH guidance; avoid high-dose single therapy during pregnancy where a multidose option is available.
Treat current sexual partners concurrently, offer testing for chlamydia, gonorrhoea, syphilis and HIV, and avoid sex for at least one week and until the patient and partners have completed treatment and follow-up.
Routine test of cure is unnecessary when symptoms resolve, but persistent or recurrent symptoms require repeat testing after an interval that avoids residual nucleic acid.
Before diagnosing resistance, verify doses, vomiting, sexual re-exposure and partner treatment; seek specialist advice for higher-dose or alternative nitroimidazole regimens.
Do not infer trichomoniasis from discharge colour alone because bacterial vaginosis, candidiasis, cervicitis and retained foreign material can overlap.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Sexual transmission

Motile T. vaginalis trophozoites pass through genital sexual contact and colonise susceptible urogenital squamous epithelium without forming an environmental cyst.

Asymptomatic carriage

Minimal inflammation in many infected people permits prolonged unrecognised carriage and repeated transmission to partners who have no obvious symptoms.

Reinfection cycle

Successful index treatment can be followed quickly by reacquisition when a current partner remains untreated or sex resumes before therapy is complete.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Epithelial adherence
Protozoa adhere to vaginal or urethral epithelium and release cytotoxic products that disrupt cells and the local microbial environment.
2
Inflammatory vaginitis
Neutrophil recruitment, epithelial damage and small mucosal haemorrhages produce soreness, discharge, raised pH and occasional punctate cervical erythema.
3
Variable host response
Differences in organism burden, microbiome and immune response explain why manifestations range from silent carriage to marked offensive inflammatory discharge.
4
Mucosal susceptibility
Inflamed epithelium and coexisting infections may increase vulnerability to acquisition or transmission of HIV and other sexually transmitted pathogens.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Vaginal discharge syndrome

Offensive yellow-green or frothy discharge with soreness, itch, dysuria or dyspareunia supports testing but does not establish the organism.

Punctate cervicitis

A strawberry cervix reflects small mucosal haemorrhages and supports trichomonal inflammation, although it is absent in most infections.

Silent urethral infection

A penile urethra may carry T. vaginalis without symptoms or may produce mild discharge and dysuria as non-gonococcal urethritis.

Upper-tract featuresRed flag

Pelvic pain, fever, abnormal bleeding and cervical or adnexal tenderness indicate possible PID and demand broader immediate care.

Persistent disease

Continuing discharge after therapy may reflect missed doses, vomiting, reinfection, untreated partners, premature testing or true antimicrobial resistance.

Red flags requiring action

Pelvic or lower abdominal pain with cervical motion, uterine or adnexal tenderness requires assessment and empirical treatment for PID.
Pregnancy with pain, bleeding, contractions, fluid loss or reduced fetal movement needs urgent maternity assessment rather than routine vaginitis follow-up.
Fever, hypotension, vomiting or peritonism suggests complicated pelvic infection or another acute abdominal diagnosis.
Persistent infection after verified adherence and partner treatment requires specialist review for reinfection, test timing and possible nitroimidazole resistance. Treat current sexual partners concurrently, offer testing for chlamydia, gonorrhoea, syphilis and HIV, and avoid sex for at least one week and until the patient and partners have completed treatment and follow-up.
Ulceration, significant contact bleeding or a mass requires examination for herpes, syphilis, trauma or neoplasia.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Trichomonas NAATFirst step
Why
Detect T. vaginalis sensitively from a vaginal or other specimen validated by the local laboratory.
Interpretation and limitations
A positive result requires patient and partner treatment; delay post-treatment NAAT enough to avoid residual nucleic-acid detection.
02
Wet-mount microscopy
Why
Identify motile trichomonads rapidly where immediate microscopy and experienced staff are available.
Interpretation and limitations
A positive motile organism supports diagnosis, but sensitivity declines quickly and a negative wet mount requires molecular testing when suspicion remains.
03
Vaginal pH and discharge microscopy
Why
Distinguish raised-pH vaginitis from acidic-pH candidiasis and identify bacterial-vaginosis features.
Interpretation and limitations
A pH above 4.5 is compatible with trichomoniasis or BV; semen, blood and cervical mucus can also raise pH.
04
Chlamydia, gonorrhoea, HIV and syphilis tests
Why
Identify clinically important co-infections and complete sexual-health care for patient and partners.
Interpretation and limitations
Use exposure sites and window periods, obtaining gonococcal culture before treatment when gonorrhoea is suspected.
05
Pregnancy test and pelvic assessment
Why
Modify counselling and recognise ectopic pregnancy or PID rather than uncomplicated vaginitis.
Interpretation and limitations
Pregnancy does not preclude metronidazole, but pain or bleeding changes urgency and may require maternity or gynaecology review.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Bacterial vaginosis

Thin fishy discharge and raised pH overlap with trichomoniasis, but BV usually has little inflammation and different partner management.

Vulvovaginal candidiasis

Intense itch, curdy discharge, vulval erythema and normal acidic pH favour Candida, although mixed infection can occur.

Cervicitis and PID

Chlamydia, gonorrhoea or M. genitalium can cause discharge, bleeding and pelvic tenderness requiring broader testing and treatment.

Retained foreign material

A retained tampon or other vaginal object can cause offensive discharge and bleeding and is identified by careful examination.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01CONFIRMTest the discharge syndromeFirst stepA patient presents with discharge, odour, irritation, dysuria or notification as a trichomonas contact.

1Ask privately about onset, discharge, pain, bleeding, urinary symptoms, pregnancy possibility, exposure sites, prior treatment and partner symptoms.
2Examine the vulva and cervix when appropriate, assess upper-tract tenderness, and obtain a validated trichomonas NAAT with wider STI samples.
3Use immediate wet microscopy as supportive testing only and send molecular testing when the wet mount is negative but suspicion continues.
4Treat or refer urgent pregnancy, PID, sepsis, ulceration or another diagnosis before routine outpatient closure.

02TREATUse systemic multidose metronidazoleMolecular or validated microscopy confirms uncomplicated T. vaginalis infection.

1Give metronidazole 400 to 500 mg orally twice daily for seven days and discuss nausea, taste disturbance and important interactions.
2Use metronidazole through pregnancy or breastfeeding when indicated, preferring the multidose course and avoiding unnecessary treatment delay.
3Arrange concurrent treatment for current partners and offer everyone appropriate chlamydia, gonorrhoea, HIV and syphilis testing.
4Advise no sexual contact for at least one week and until both patient and partners have completed treatment and scheduled follow-up.

03PERSISTResolve recurrent or persistent infectionSymptoms continue or a properly timed repeat test remains positive after an apparently completed course.

1Verify the exact medicine, doses, retained tablets, adherence, sexual re-exposure and whether every current partner completed effective treatment.
2Repeat a validated assay after an adequate interval and reassess BV, candidiasis, cervicitis, foreign body and non-infective vulval disease.
3If reinfection and testing artefact are unlikely, seek specialist advice before a higher-dose metronidazole or tinidazole regimen.
4Recheck pregnancy, liver disease, neurological symptoms and interacting medicines before any intensified nitroimidazole course.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Provides systemic urogenital treatment and higher cure rates than the older single 2 g regimen.

Metronidazole multidose

Take 400 to 500 mg orally twice daily for seven days for uncomplicated trichomoniasis.

Review warfarin, lithium, liver disease and neurological symptoms; use in pregnancy when indicated and follow current product advice about alcohol.

Offers a less effective but sometimes practical alternative after an individual adherence assessment.

Metronidazole single dose

A 2 g oral single dose is an alternative when adherence to multidose therapy is not achievable.

Avoid high-dose therapy in pregnancy where possible, anticipate gastrointestinal intolerance, and do not use topical gel as a substitute.

Provides an alternative nitroimidazole option for selected confirmed persistent or resistant T. vaginalis infection.

Tinidazole specialist regimen

Dose and duration must follow the specialist persistent-infection pathway after reinfection and adherence have been assessed.

Avoid unsupervised empirical use; check pregnancy, breastfeeding, liver disease, neurological toxicity, interactions and current product information.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Persistent transmission

Untreated asymptomatic partners maintain the infection chain and expose the patient to repeated symptomatic episodes after apparently successful therapy.

Pregnancy association

Infection is associated with adverse reproductive outcomes, supporting diagnosis and effective pregnancy-compatible therapy when clinically identified.

Upper-tract inflammation

Trichomonas may coexist with cervical pathogens and is associated with PID, so pelvic pain requires examination rather than a vaginitis-only label.

Treatment persistence

Reinfection, non-adherence and occasional nitroimidazole resistance can produce ongoing infection requiring specialist reassessment and an alternative regimen.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Confirm symptom resolution, completion of every dose and treatment of current partners before attributing recurrence to resistance.
Check that abstinence continued for at least one week and until both the patient and partners had completed therapy and follow-up.
Do not arrange routine test of cure after uncomplicated resolved disease, but investigate persistent symptoms with an appropriately timed validated assay.
Review pregnancy or maternity concerns, adverse drug effects and important interactions during the seven-day metronidazole course.
Provide a rapid return route for pelvic pain, fever, pregnancy bleeding, worsening discharge or new genital ulceration.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Wet mount misses infection

Motility and sensitivity fall after collection, so a negative slide does not safely exclude trichomoniasis when NAAT is available.

Topical treatment is inadequate

The organism can occupy urethral and vaginal sites that intravaginal metronidazole does not reliably reach or eradicate.

Partners may be asymptomatic

Silent carriage is common, making concurrent partner treatment more important than using symptoms to decide who receives care.

Pregnancy permits treatment

Metronidazole can be used throughout pregnancy under BASHH guidance; withholding effective therapy solely because of gestation is inappropriate.

Persistence has several causes

Missed doses, vomiting, renewed exposure, untreated contacts and early repeat testing are more common explanations than proven drug resistance.

11Common pitfallsFrequent interpretation and management errors.

01
Diagnosing trichomoniasis solely from frothy or green discharge without organism testing.
02
Using topical metronidazole for an infection that requires systemic urogenital treatment.
03
Leaving a current asymptomatic partner untreated and creating preventable reinfection.
04
Avoiding all metronidazole in pregnancy despite current BASHH guidance supporting treatment.
05
Repeating NAAT too soon and mistaking residual nucleic acid for viable persistent infection.
06
Escalating doses before checking adherence, vomiting, partner therapy and sexual re-exposure.

Find your next topic