Etiology of nongonococcal nonchlamydial urethritis.

The majority of cases of acute nongonococcal urethritis (NGU) are due to causes other than infection with Chlamydia trachomatis. Pathogens implicated as causes of nonchlamydial nongonococcal urethritis (NCNGU) include Mycoplasma genitalium, Ureaplasma urealyticum, Trichomonas vaginalis, and primary infection with herpes simplex virus. In a majority of cases of acute NCNGU, no pathogen can be isolated. The etiology of chronic NCNGU is unknown.