What is the most likely causative organism for epididymitis in men over 35 years?

In men over 35 years of age, the most likely causative organism for epididymitis is Escherichia coli. This age group is more likely to experience epididymitis due to urinary tract infections (UTIs) rather than sexually transmitted infections (STIs). E. coli is one of the most common pathogens responsible for UTIs, which can ascend to the epididymis and cause inflammation.

In younger men, particularly those under 35, Chlamydia trachomatis and Neisseria gonorrhoeae are more commonly associated with epididymitis due to sexual transmission. However, in the older population, the prevalence of E. coli rises significantly, making it the primary organism in cases of epididymitis, particularly when there are associated urinary symptoms or prostate issues.

Staphylococcus aureus is less commonly implicated in epididymitis and is typically associated with scenarios involving hematogenous spread or skin infections rather than urinary issues. Therefore, the likelihood of E. coli being the causative agent in men over 35 is supported by the commonality of UTIs, the age-related factors affecting the male population, and the relative prevalence of different pathogens in different demographics.