This motile flagellated protozoan infests the vagina and labial area in the female and the prostate and urethra of the male. Estrogen effect on vaginal epithelial cells is a predisposing factor toward infestation in females, so that trichomoniasis is uncommon before puberty or after menopause. The infection is usually transmitted during sexual intercourse, although some cases are not. In one study, 70% of men examined less than 48 hours after intercourse with an infected woman were found to also be infected. The incubation period before clinical symptoms is 4-28 days. There is a concurrent significantly higher incidence of other sexually transmitted diseases. Symptoms in the female most often consist of vaginal discharge, with the differential diagnosis including infection by Trichomonas, Gardnerella vaginalis, and Candida albicans. The disease is usually asymptomatic in males. However, one study found that 15%-20% of male urethritis resistant to standard therapy was due to Trichomonas. Also, 25%-50% of culture-positive female patients are asymptomatic, although there is some question as to whether these are true infections or the equivalent of bacterial colonization without infection.

Culture has been considered the gold standard for diagnosis. However, culture needs special media and takes 2-7 days. Some reports indicate that culture sensitivity is 86%-97%. One report found that only 60% of male urethral cultures were positive. A wet preparation collected by swab from the posterior vaginal fornix and placed into a drop of 0.9% saline is the most simple and rapid method of diagnosis. The specimen should not be taken from the endocervix, since this area is rarely involved. If the wet preparation cannot be made and read immediately, the swab can be inoculated into a standard bacteriologic transport medium. Compared to culture, the wet preparation detects about 50%-70% (range, 15%-89%) of patients but correlates much better with symptomatic infection than does culture. One study from the Communicable Disease Center found detection rates on wet mount varied from 62%-92% from different technologists. The organism can also be detected with stained smears using either Wright’s stain or Papanicolaou stain. Sensitivity of the Papanicolaou smear compared to culture is about 50%-60% (range, 34%-70%), in addition to a considerable false positive rate in some laboratories. The diagnosis sometimes is made by accident from microscopic examination of urine sediment during a urinalysis if the organisms are still motile. Nonmotile Trichomonas organisms round up and become very difficult to differentiate from white blood cells or small epithelial cells in urine or wet-mount preparations. If the organisms appear in the urine of female patients, the urine probably was contaminated by vaginal or labial contact. Fluorescent immunoassay kits that can be applied to prepared slides are now commercially available with sensitivities compared to culture of 82%-86%. There also are commercial available enzyme immunoassay (EIA) methods applied directly to prepared slides, with sensitivity stated as 81%-82%. LA tests are recently available, but little independent evaluation has appeared. A nucleic acid probe has also been reported, with a sensitivity in one study being 83% versus culture.