Trichomonads are motile, flagellate, protozoan organisms known to cause a diverse spectrum of diseases in humans. Most of these diseases are rare. The single exception is Trichomonas vaginalis, the most significant of these parasites, which infects between 3 and 5 million American women each year. The organism causes an inflammation of the vaginal wall, or vaginitis, in women who contract this disease. The disease is usually sexually transmitted and the incidence is high particularly in populations at risk for other venereal diseases, such as those attending clinics for sexually transmitted diseases, those with multiple sexual partners, and those infected with HIV. T. vaginalis also causes genital infections in men; because these tend to be asymptomatic, the true incidence of infection in this population is unknown.

The clinical presentation of trichomoniasis is variable. It is estimated that between one fourth and one half of infected women are asymptomatic; in symptomatic women, the...