Trichomoniasis (trih-kuh-muh-NIE-uh-sus) is caused by a one-celled protozoan parasite called Trichomonas vaginalis.

Incidence and Transmission

Trichomoniasis is a common STI in both women and men. Between 7 and 8 million new cases of trichomoniasis occur each year in the United States (Centers for Disease Control, 2009k). The primary mode of transmission of this infection is through sexual contact. Women can acquire it from infected men via penile-vaginal intercourse and from infected women via vulva-to-vulva contact; however, men usually contract tricho­moniasis only from infected women via coitus (Centers for Disease Control, 2009k).