Most Common Cause of Epididymo-Orchitis
The most common cause of epididymo-orchitis depends critically on patient age: in sexually active men under 35 years, Chlamydia trachomatis and Neisseria gonorrhoeae are the predominant pathogens, while in men over 35 years, enteric gram-negative bacteria (primarily E. coli) are most common. 1, 2
Age-Based Etiology
Men Under 35 Years (Sexually Active)
- Sexually transmitted pathogens dominate: Chlamydia trachomatis and Neisseria gonorrhoeae account for the majority of cases in this age group 1, 3
- These infections typically occur via retrograde propagation through the vas deferens from urethritis 4
- Epididymitis in this population is usually accompanied by urethritis, which is often asymptomatic 1
- Important caveat: Men who practice insertive anal intercourse may develop epididymitis from sexually transmitted enteric organisms like E. coli 1, 3
Men Over 35 Years
- Enteric gram-negative bacteria predominate: E. coli and other coliform bacteria are the primary pathogens 1, 3, 5
- These infections are typically associated with urinary tract abnormalities, particularly bladder outlet obstruction from benign prostatic hyperplasia or urethral stricture 6, 4, 5
- Gram-positive organisms including Staphylococcus aureus, Enterococcus, and Group B streptococci can also cause infection 1
- The route of infection involves reflux of urine into the ejaculatory ducts secondary to anatomical obstruction 3, 4
Prepubertal Children
- Etiology is largely unknown, but reflux of urine into the ejaculatory ducts is considered the most common mechanism 3
- Enterobacteria are the usual causative organisms when infection is present 4
Less Common Causes
Viral Orchitis
- Mumps virus is the most frequent viral cause of orchitis 1
- Other viral pathogens include Coxsackie virus, rubella virus, Epstein-Barr virus, and varicella zoster virus 1
- Viral orchitis typically occurs via hematogenous dissemination 4
Fungal and Mycobacterial Infections
- Systemic fungal diseases (Blastomyces dermatitidis, Histoplasma capsulatum, Coccidioides immitis) can involve the epididymis or testis 1
- Mycobacterium tuberculosis may also affect these sites, though this is uncommon 1
- These require specific communication with the laboratory to ensure proper culture medium selection 1
Clinical Pitfalls to Avoid
- Do not rely solely on urinalysis in men under 35 years: STI-related epididymitis frequently presents without significant pyuria, and urinalysis misses the majority of cases in younger men 2
- Obtain urethral swab testing rather than just urine studies in sexually active men under 35, as these infections originate from urethral pathogens 2
- Current tests for C. trachomatis are not sufficiently sensitive to exclude infection even when negative, so empiric treatment may still be indicated 2
- Always consider testicular torsion in the differential diagnosis, particularly in adolescents and when pain onset is sudden—this is a surgical emergency requiring intervention within 4-6 hours 1, 6