The epididymis is a system of tubules around the testicular poles draining and carrying the sperms through the vas deferens into the prostate (seminal vesicles) where are stored. Epididymitis is, in general, an acute infection of the epididymis. The bacteria (infection) inversely travels the sperm path (vas deferens), which connects the prostate to the epididymis. In fact, the infection of the epididymis may represent a complication of prostatitis.

Acute epididymitis has a good chance of being an STI since the most frequent bacteria are Chlamydia Tracomatis and Neisseria Gonorrhoeae. Another frequently involved bacteria are the Enterobacteriaceae (typically E. coli). Men who have anal intercourse and those with abnormalities of the urinary tract resulting in bacteriuria are at higher risk of epididymitis caused by Enterobacteriaceae.

The mumps virus should be considered if there are viral prodromal symptoms and salivary gland enlargement. Tuberculous epididymitis may occur, typically as chronic epididymitis, in high-risk groups such as men with immunodeficiency and those from high prevalence countries, it frequently results in a discharging scrotal sinus.

Symptoms of acute epididymitis are pain, swelling, and increased temperature of the epididymis, which may involve the testis and scrotal skin. Sometimes the urination may be painful, the semen can be bloody and fever and chills can also occur. As a cause of acute scrotal pain, acute epididymitis has to be discriminated from the torsion of the spermatic cord (testicular torsion) in particular in boys and young men.

Scrotal pain, in general, is a good reason to see a doctor get a correct diagnosis and the right treatment and avoid complications.