[edit] Causes

Infection is the most common cause of epididymitis. The bacteria in the urethra back-track through the urinary and reproductive structures to the epididymis. There can be associated urethritis (inflammation of the urethra). Rarely, the infection reaches the epididymis via the bloodstream.
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.[1] Less common microbes include Ureaplasma, Mycobacterium, and cytomegalovirus, or Cryptococcus in patients with HIV infection. E. coli is more common in boys before puberty, the elderly and homosexual men.
Non-infectious causes are also possible. Reflux of sterile urine (urine without bacteria) through the ejaculatory ducts may cause inflammation with obstruction. In children, it may be a response following an infection with enterovirus, adenovirus or Mycoplasma pneumoniae.
Epididymitis can also be caused by genito-urinary surgery, including prostatectomy and urinary catheterization. Congestive epididymitis is a long-term complication of vasectomy.[2][3] Chemical epididymitis may also result from drugs such as amiodarone.[4]