Causes of Epididymitis and Orchitis
Age-Dependent Etiology
The causative organisms of epididymitis and orchitis are primarily determined by patient age, with sexually transmitted infections predominating in younger men and enteric bacteria in older men.
Men Under 35 Years of Age (Sexually Active)
- Chlamydia trachomatis and Neisseria gonorrhoeae are the predominant pathogens in sexually active men under 35 years, representing the most common causes of epididymitis in this age group 1, 2.
- These sexually transmitted infections typically cause urethritis-associated epididymitis, often presenting without significant pyuria 3.
- Among men in this age group diagnosed with epididymitis or orchitis in the emergency department, chlamydia (12.3%) was more common than gonorrhea (3.1%) 4.
- Sexually transmitted Escherichia coli infection can also occur among men who have sex with men who are the insertive partners during anal intercourse 5.
Men Over 35 Years of Age
- Enteric gram-negative bacteria, primarily E. coli, are the most common cause of epididymo-orchitis in men over 35 years 1, 6.
- These infections are typically associated with urinary tract infections and often occur in the context of functional bladder outlet problems such as benign prostatic hyperplasia or urethral stricture disease 6.
- Other enteric organisms include Klebsiella, Pseudomonas, Serratia, and Streptococcus species 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 5.
Viral Causes of Orchitis
- 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 1.
- Viral orchitis typically occurs via hematogenous dissemination rather than retrograde spread through the vas deferens 7.
Less Common Infectious Causes
- Systemic fungal diseases, such as Blastomyces dermatitidis, Histoplasma capsulatum, and Coccidioides immitis, can involve the epididymis or testis and require specific laboratory testing 1.
- Fungi and mycobacteria are more likely to cause epididymitis in immunosuppressed patients, including those with HIV infection, than in immunocompetent patients 5.
- Tuberculous or fungal epididymitis should be considered when swelling and tenderness persist after completion of standard antimicrobial therapy 5.
Route of Infection
- The main route of access to the epididymis is retrograde propagation through the vas deferens from the urethra or bladder 7.
- In sexually transmitted cases, the infection originates from urethral pathogens rather than urinary tract bacteria, which is why urethral swab testing is more diagnostic than urinalysis alone in younger men 3.
- Hematogenous spread occurs primarily with viral causes and occasionally with systemic fungal infections 7.
Critical Clinical Pitfall
- In sexually active men under 35 years, urethral swab testing rather than just urine studies must be obtained, as these infections originate from urethral pathogens and current tests for C. trachomatis are not sufficiently sensitive to exclude infection even when negative 1, 3.
- Relying solely on urinalysis misses the majority of STI-related epididymitis cases in younger men 3.