There is spread of infection locally, either from the urinary tract (urethra or bladder) through the ejaculatory duct, seminal vesicle and the vas deferens. Infection can also spread from other sites via the blood or lymphatics. This causes inflammation involving the epididymis (epididymitis), the testicle (orchitis) or both (epididymo-orchitis). There can be non-infectious causes which include drugs (e.g. amiodarone), vascular (Behçet’s disease), autoimmune (Sarcoidosis) and others. Mumps is another causative agent to consider in the appropriate clinical context.

STIs: Most commonly C. trachomatis or N. gonorrhoea in the sexually active, and epididymo-orchitis may present as a progression of untreated infections. Enteric coliforms are implicated MSM patients and T. pallidum is a rarer cause of infection.

UTIs: Commonly coliforms, with catheterisation being a precipitating factor. Also consider underlying urological issues such as calculus or obstruction. Rarer causes could include M. tuberculosis with a local (e.g. renal, prostatic) infectious source.