FFinalistSouthampton · 2027
Sexual health
AKT · Sexual health/Vaginitis / discharge

Trichomonas vaginalis

Trichomonas vaginalis — a flagellated protozoan

Overview

A sexually transmitted protozoal infection causing vaginitis and urethritis. It is the one "discharge" diagnosis that is unequivocally an STI, so partner notification and a full sexual health screen are part of treating it — which is what separates it from bacterial vaginosis and candidiasis in the exam.

Recognise

  • Offensive, frothy, yellow-green vaginal discharge — the classic description
  • Vulval itch, soreness, dysuria and superficial dyspareunia
  • Strawberry cervix (punctate cervical haemorrhages) — highly suggestive but present in a minority
  • Vaginal pH above 4.5
  • Men are usually asymptomatic, or have urethritis with a scanty discharge
  • Up to half of infected women have no symptoms at all

Red flags

  • Infection in pregnancy is associated with preterm birth and low birth weight — treat, and screen for co-existing STIs

Differentials & how to tell them apart

Bacterial vaginosisThin grey-white discharge with a fishy odour, pH >4.5, clue cells — NOT itchy and NOT an STI
Vulvovaginal candidiasisThick white "cottage cheese" discharge with intense itch and a NORMAL pH (<4.5)
Chlamydia / gonorrhoea cervicitisMucopurulent cervicitis with contact bleeding; diagnosed on NAAT, no trichomonads
Retained foreign body (e.g. tampon)Extremely offensive discharge that resolves on removal

Investigations

NAAT is the test of choice where available (highest sensitivity). Wet-mount microscopy of a high vaginal swab from the posterior fornix shows motile flagellated trichomonads but is far less sensitive, and sensitivity falls quickly once the sample cools. Vaginal pH. Full STI screen — chlamydia, gonorrhoea, HIV and syphilis — because co-infection is common.

Management

Metronidazole 400–500 mg orally twice daily for 5–7 days, with partner notification

  1. 1Metronidazole as above. Advise abstaining from sex until both the patient and their partner(s) have completed treatment.
  2. 2Partner notification is essential — current partners should be treated EPIDEMIOLOGICALLY, whether or not they test positive, or reinfection is near-certain. Offer a full STI screen including HIV.Gate: Persistent symptoms after treatment → confirm adherence and partner treatment, then re-test; consider high-dose metronidazole on specialist advice
  3. 3Counsel on alcohol: a disulfiram-like reaction with metronidazole means avoiding alcohol during treatment and for 48 hours afterwards.
Metronidazole 400–500 mg PO BD for 5–7 days — First-line. A 2 g single dose is an alternative where adherence is a concern, but has slightly higher failure rates
Metronidazole (treatment in pregnancy) — Treat in pregnancy; avoid the high-dose 2 g single-dose regimen. Discuss breastfeeding timing

Key points

Three discharges, three discriminations. Trichomonas is frothy, green and itchy with a raised pH. Bacterial vaginosis is grey, fishy and NOT itchy with a raised pH. Candida is white, curd-like and intensely itchy with a NORMAL pH. Only trichomonas requires partner treatment.

Monitor & prognosis

Test of cure is not routine if symptoms resolve; re-test if symptoms persist or recur.

Cure rates over 95% with treatment of both partners. Reinfection is the usual reason for apparent failure.

Source: BASHH guidelines · NICE CKS — trichomoniasis