In adults it is virtually always transmitted sexually. Untreated, infection may persist in women for years and in men for many months. In females the organisms can be isolated from the vagina, urethra and paraurethral glands. In males infection usually occurs in the urethra although trichomonas has been isolated from the subpreputial sac and penile lesions.
Perinatal transmission can occur.
Trichomonas is widespread., although in urban Australia there has been a considerable decline in incidence and prevalence during the past decade. The highest incidence is among sexually active 16 to 35 year olds. Infection beyond the first year of life should suggest sexual contact. Trichomonas may coexist with gonococcal infection. If trichomoniasis is diagnosed, a full STI assessment is recommended.