The most common cause of epididymitis is

Epididymitis is most common in young men ages 19 to 35. Chlamydia is the most common cause in sexually active men younger than 35 years (accounting for up to 50% of cases). Infections with urinary coliforms (eg, E coli, Pseudomonas species, Proteus species, Klebsiella species) are the most common cause in children and in men older than 35 years. Reference : page 1383 Bailey and Love's sho practice of surgery 25th edition