Trichomoniasis is a common, curable sexually transmitted infection (STI) caused by a microscopic parasite called Trichomonas vaginalis. It mainly infects the urogenital tract (vagina, urethra, sometimes prostate) and often causes no symptoms, especially in men, which makes it easy to spread.

Main symptoms

In women, trichomoniasis often causes vaginal discharge that may be thin or frothy and can be white, yellow, or green with an unpleasant or “fishy” odor. There may also be genital itching or burning, pain with urination, pain during sex, and sometimes lower abdominal discomfort.

In men, most infections are asymptomatic, but some have urethral discharge, burning when urinating or after ejaculation, or irritation inside the penis. Because so many people have no symptoms, testing is important if a partner is diagnosed or if there is any concern about STI exposure.

How it spreads and risks

Trichomoniasis spreads through genital contact, most commonly during vaginal sex without a condom, and can pass between penis and vagina or vagina to vagina. People can transmit the infection even when they have no symptoms. Infection is linked to higher risk of acquiring or transmitting HIV and to pregnancy problems such as preterm birth or low-birth-weight infants.

Diagnosis and treatment

Diagnosis is made by testing vaginal fluid or urine using microscopy, culture, or modern rapid tests that detect the parasite’s DNA. Treatment is with prescription antibiotics from the nitroimidazole group, most commonly metronidazole or tinidazole, given either as a single larger dose or over several days. Sexual partners should be treated at the same time, and sex should be avoided until all partners complete treatment and symptoms resolve to reduce reinfection.

Prevention and when to seek care

Risk can be reduced by correct and consistent condom use, limiting number of sexual partners, regular STI screening, and avoiding douching, which can disrupt normal vaginal flora. Anyone with new genital discharge, itching, or pain with urination or sex, or whose partner is diagnosed with trichomoniasis, should see a healthcare professional or STI clinic for testing and treatment.