BASHH Guidelines

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Trichomonas vaginalis (TV) is a flagellated protozoon.

In women it is found in the vagina, urethra and paraurethral glands. Urethral infection is present in 90% of infected women, although the urethra is the sole site of infection in less than 5% of cases.

In men infection is usually of the urethra, although trichomonads have been isolated from the subpreputial sac and lesions of the penis.

Due to site specificity, infection can only follow intravaginal or intraurethral inoculation of the organism.

Clinical Features



  • 10-50% are asymptomatic.
  • Commonest symptoms are vaginal discharge, vulval itching, dysuria, or offensive odour.
  • Occasionally, low abdominal discomfort or vulval ulceration.


  • 15-50% are asymptomatic and usually present as sexual partners of infected women.
  • In symptomatic men, the commonest presentation is urethral discharge and/or dysuria.
  • Other symptoms include urethral irritation, urinary frequency and rarely purulent urethral discharge or prostatitis.




  • Up to 70% have vaginal discharge, from thin and scanty to profuse and thick.
  • Classical frothy yellow discharge occurs in 10-30%.
  • Other signs include vulvitis, vaginitis and 2% of patients have strawberry cervix.


  • 20-60% men have urethral discharge - usually small or moderate amounts only, and/or dysuria.
  • Rarely balanoposthitis.




  • There is evidence that TV is associated with preterm delivery and low birth weight in pregnancy (III).
  • TV infection at delivery may predispose to maternal postpartum sepsis.
  • Conflicting evidence regarding TV treatment in pregnancy. Screening of asymptomatic individuals is therefore not recommended (I&II, A).


  • Growing evidence that TV infection may enhance HIV transmission and there may be an increased risk of TV infection in those that are HIV positive.



  • TV testing should should be done in women complaining of vaginal discharge or vulvitis, or found to have evidence of vulvitis, and/or vaginitis on examination.
  • Swab taken from posterior fornix during speculum examination (III,B)
  • Self-taken swabs are likely to give equivalent results.
  • Nucleic acid amplification tests (NAAT) if available.



  • TV testing should be done for TV contacts and considered in those with persistent urethritis.
  • Testing in men is recommended for TV contacts, and should be considered in those with persistent urethritis.
  • Urethral culture or culture of first void urine will diagnose 60-80% of cases (III, B).



  • Detection of motile trichomonads by light-field microscopy. Vaginal discharge is collected with swab or loop, mixed with a drop of saline on a glass slide and coverslip placed on top.
  • The wet preparation should be read within 10 minutes of collection. Sensitivity is highest in women presenting with vaginal discharge and a visualisation of motile trichomonads in these women indicates the presence of infection.


Point of care tests (IIb, B)

  • OSOM Trichomonas Rapid Test (Genzyme Diagnostics, USA) has demonstrated a high sensitivity and specificity


Culture (IIb, B)

  • Culture has a higher sensitivity compared to microscopy and can detect TV in men.


Molecular detection (IIb, B)

  • NAATs offer the highest sensitivity. They should be the test of choice where resources allow and are becoming the current ‘gold standard’.


General Advice

  • Full explanation of diagnosis with written information.
  • Screening for other STIs


Recommended regimes (Ia, A)

  • Metronidazole 2g orally in a single dose or
  • Metronidazole 400-500mg twice daily for 5-7 days

 Alternative regimens

  • Tinidazole 2g orally in a single dose


Special Considerations

Pregnancy and breast feeding

  • It is not known if metronidazole has any effect on pregnancy outcomes. Meta-analyses have concluded that there is no evidence of teratogenicity during the first trimester of pregnancy (Ia).
  • Metronidazole can be used in all stage of pregnancy and during breast feeding. Symptomatic women should be treated at diagnosis, although some clinicians have preferred to defer treatment until the second trimester.
  • The BNF advises against high dose regimens in pregnancy.
  • Metronidazole enters breast milk and may affect its taste. Avoid high doses if breastfeeding or if using a single dose of metronidazole, breastfeeding should be discontinued for 12-24 hours to reduce infant exposure.
  • Tinidazole’s safety in pregnant women has not been well-evaluated. The manufacturer states that the use of tinidazole in the first trimester is contraindicated.

HIV positive individuals

  • Few data available, but a recent randomized clinical trial demonstrated that a 2g single oral dose of metronidazole was not as effective as 500mg of metronidazole twice daily for 7 days among HIV-infected women


Reactions to treatment

  • Patients should be advised not to take alcohol for the duration of treatment and for at least 48 hours, (72 hours for tinidazole) afterwards because of the possibility of a disulfiram-like reaction.



  • It is unknown whether there is cross reactivity between the two agents.

In cases of true allergy, desensitization to metronidazole could be considered.


Sexual contacts

  • Sexual contact(s) should be treated simultaneously and patients should be advised to abstain for at least one week until they and their partner(s) have completed treatment and follow-up.
  • Any partners within the four weeks prior to presentation should be screened for the full range of STIs and treated for TV (Ib A).
  • Male TV contacts with urethritis may be treated initially for TV and repeat urethral smear before treating additionally for NGU (III)
  • Male partners of women with treatment failure should be evaluated and treated with either metronidazole 400-500mg twice daily for 7 days or tinidazole 2g single dose (expert opinion). 


Treatment failure

  • Persistent or recurrent TV is due to inadequate therapy, re-infection, or resistance. Therefore check compliance, vomiting post metronidazole and assess for risk of reinfection.
  • Resistance tests can be of clinical benefit. Resistance data from the UK are lacking due to the absence of a metronidazole resistance testing service.
  • Treatment protocol for non-response to standard TV therapy
    Repeat course of 7-day standard therapy

Metronidazole 400-500mg twice daily for 7 days (III)

For patients failing this second regimen:

  1. Higher dose course of nitroimidazole

Metronidazole or tinidazole 2g daily for 5-7 days or
Metronidazole 800mg three times daily for 7 days (III)

For those failing this third regimen, resistance testing should be performed if available. If resistance testing is not available high dose tinidazole regimens may be considered:

  1. Very high dose course of tinidazole
    Tinidazole 1g twice or three times daily, or 2g twice daily for 14 days +/- intravaginal tinidazole 500mg twice daily for 14 days (III)
  2. Other treatments with some reported success (IV/anecdotal)
    Paromomycin* intravaginally 250mg once or twice daily for 14 days

Furazolidone* intravaginally 100mg twice daily for 12-14 days

Acetarsol* pessaries 500mg nocte for 2 weeks
6% Nonoxynol–9* pessaries nightly for 2 weeks
*The medicines suggested for use in treatment failure are unlicensed products and may not be readily available for purchase in the UK.


Follow up

  • Test of cure only recommended if the patient remains symptomatic following treatment, or if symptoms recur. (IV, C)

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