Trichomoniasis

Trichomoniasis is caused by Trichomonas vaginalis, a flagellated protozoan, and is a genuinely sexually transmitted infection, distinct from bacterial vaginosis and candidiasis. It is one of the most common curable STIs globally and is frequently asymptomatic, particularly in men, who typically act as an under-recognized reservoir for transmission.

Classically a frothy, yellow-green, malodorous discharge with vulvovaginal irritation, dysuria, and dyspareunia. The "strawberry cervix" (punctate hemorrhages on the cervix) is a classic but insensitive examination finding, seen in only a minority. Men are usually asymptomatic, though urethritis, mild dysuria, or discharge can occur.

• NAAT testing (vaginal swab in women, first-void urine or urethral swab in men) is the most sensitive and now widely preferred method where available
• Wet mount microscopy showing motile trichomonads has high specificity but lower sensitivity (roughly 50 to 70%), and requires prompt examination given organisms lose motility quickly once the sample cools
• Vaginal pH is typically elevated (above 4.5), similar to BV
• Given trichomoniasis is a true STI, screening for other STIs (chlamydia, gonorrhea, syphilis, HIV) should be offered, and this diagnosis should prompt partner notification and treatment

• Metronidazole 2 g PO as a single dose, or metronidazole 400 to 500 mg PO bd for 5 to 7 days (the multi-day course is generally preferred, with somewhat higher cure rates in some studies, particularly for women)
• Tinidazole 2 g PO single dose is an effective alternative where available
• Treat all sexual partners simultaneously, regardless of symptoms, and advise abstinence until both partners have completed treatment and are symptom free (generally 7 days)
• Avoid alcohol during and for 48 hours after metronidazole (72 hours after tinidazole)
• In pregnancy, oral metronidazole is used (considered safe at standard doses at any gestation), given symptomatic infection is associated with preterm birth and low birth weight; treatment of asymptomatic infection in pregnancy has not clearly shown benefit in preventing these outcomes but symptomatic women should be treated
• Treatment failure: retreat with metronidazole 400 to 500 mg PO bd for 7 days if single dose was used initially; persistent failure after appropriate partner treatment and adherence raises consideration of resistance, and higher dose metronidazole or tinidazole regimens are used under specialist guidance

Referral: sexual health services for full STI screening, partner notification, and management of treatment failure.