Definition/diagnostic criteria Trichomonas infection, also known as trichomoniasis, is a sexually transmitted infection (STI) caused by the protozoan parasite Trichomonas vaginalis. It primarily affects the urogenital tract in both males and females. The clinical diagnosis of trichomoniasis is based on clinical symptoms and laboratory confirmation.

Epidemiology Trichomonas infection is a common STI worldwide, including the UK. It is estimated that over 180 million people are infected globally each year. In the UK trichomoniasis is less common than other STIs, such as chlamydia and gonorrhoea. However, its prevalence is on the rise, especially among specific high-risk groups.

Clinical features:

  • Female patients may present with vaginal discharge, vulvar itching, dysuria and lower abdominal pain.
  • Males may experience urethral discomfort, itching and discharge.
  • Many infected individuals can be asymptomatic.

Investigations: The diagnosis of trichomoniasis should ideally be confirmed by a sexual health specialist via microscopic examination of vaginal/urethral discharge, culture or PCR testing.

Treatment The recommended treatment for trichomoniasis in the UK is metronidazole. Current guidelines advise 400–500 mg twice daily for 5–7 days or a  single oral dose of 2 grams for both males and females (not if pregnant or breastfeeding).

  • Patients should abstain from alcohol during treatment and for 48 hours afterward, as metronidazole can cause a disulfiram-like reaction with alcohol.
  • Sexual partners should also be treated simultaneously to prevent reinfection. Contact tracing and follow-up are part of routine care.
  • Patients should be advised to avoid sexual intercourse for at least one week and until they and their partner(s) have completed treatment and follow-up.

Prognosis With appropriate treatment symptomatic relief is usually rapid, with a noticeable improvement within a few days.

Further reading

Published: 5th January 2024 Updated: 16th February 2024

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