What is the common cause of epididymitis in patients under 40 years old?

Epididymitis in patients under 40 years old is most commonly associated with sexually transmitted infections, particularly gonorrhea and chlamydia. These pathogens are prevalent in younger sexually active men, and both are known to cause inflammation of the epididymis. The route of transmission typically involves direct inoculation during sexual activity, leading to inflammation and symptoms such as scrotal pain and discomfort.

Although other causes of epididymitis exist, such as infections from gram-negative rods associated with urinary tract infections or mumps virus in children, they are less prevalent in the specific demographic of young men. Mumps, for instance, is not as common now due to widespread vaccination. Prostatitis can contribute to epididymitis but is less likely the primary infectious etiology in this age group. Thus, the association of gonorrhea and chlamydia with sexually active young males confirms their role as the most common cause of epididymitis in this population.