In sexually active men, Chlamydia trachomatis is responsible for two-thirds of cases, followed by Neisseria gonorrhoeae and E. coli (or other bacteria that cause urinary tract infection
). Particularly among men over age 35 in whom the cause is E. coli, epididymitis is commonly due to urinary tract obstruction. Less common microbes include Ureaplasma, Mycobacterium, and cytomegalovirus, or Cryptococcus in patients with HIV infection. E.