Epididymo-Orchitis Etiology and Diagnosis

Age-Based Etiology

In sexually active men under 35 years, Chlamydia trachomatis and Neisseria gonorrhoeae are the predominant pathogens, according to the Centers for Disease Control and Prevention guidelines 1, 2
In men over 35 years, enteric gram-negative bacteria, primarily E. coli, are the most common cause of epididymo-orchitis, as recommended by the Infectious Diseases Society of America 1

Mumps virus is the most frequent viral cause of orchitis, with other viral pathogens including Coxsackie virus, rubella virus, Epstein-Barr virus, and varicella zoster virus, as reported by the Clinical Infectious Diseases journal 1
Systemic fungal diseases, such as Blastomyces dermatitidis, Histoplasma capsulatum, and Coccidioides immitis, can involve the epididymis or testis, and require specific laboratory testing, as recommended by the Clinical Infectious Diseases journal 1

The Centers for Disease Control and Prevention recommends obtaining urethral swab testing rather than just urine studies in sexually active men under 35, as these infections originate from urethral pathogens 2
The American Urological Association advises considering testicular torsion in the differential diagnosis, particularly in adolescents and when pain onset is sudden, as this is a surgical emergency requiring intervention within 4-6 hours 2

Sexually transmitted Escherichia coli infection can occur among men who have sex with men who are the insertive partners during anal intercourse, as reported by the MMWR Recommendations and Reports 3
Fungi and mycobacteria are more likely to cause epididymitis in immunosuppressed patients, including those with HIV infection, than in immunocompetent patients, according to the MMWR Recommendations and Reports 4
Tuberculous or fungal epididymitis should be considered when swelling and tenderness persist after completion of standard antimicrobial therapy, as suggested by the MMWR Recommendations and Reports 4
Nonsexually transmitted epididymitis associated with urinary tract infections caused by gram-negative enteric organisms is more common among men who have recently undergone urinary tract instrumentation or surgery, as reported by the MMWR Recommendations and Reports 3