What are the causes of epididymo-orchitis in a 31-year-old man?

Causes of Epididymo-Orchitis in a 31-Year-Old Man

In a 31-year-old sexually active man, epididymo-orchitis is most commonly caused by Chlamydia trachomatis and Neisseria gonorrhoeae, which are sexually transmitted pathogens that typically ascend from the urethra. 1, 2, 1

Age-Stratified Etiology

The causative organisms differ significantly based on age, making this a critical factor in determining the likely pathogen:

For Men <35 Years (Including Your 31-Year-Old Patient):

• Primary pathogens: C. trachomatis and N. gonorrhoeae 1, 2, 1, 3
• Secondary consideration: Sexually transmitted enteric organisms (particularly E. coli) in men who are insertive partners during anal intercourse 1, 2, 1
• Key clinical feature: Usually accompanied by urethritis, which is often asymptomatic 1, 2

For Men >35 Years:

• Primary pathogens: Gram-negative enteric organisms (predominantly E. coli) causing urinary tract infections 1, 2, 1, 3
• Risk factors for this age group:
  • Recent urinary tract instrumentation or surgery
  • Anatomical abnormalities of the urinary tract
  • Bladder outflow obstruction 1, 2

Additional Causative Organisms

Beyond the common bacterial causes, several other pathogens can cause epididymo-orchitis, though they are less frequent:

Viral Causes:

• Mumps virus (most common viral cause of orchitis) 3
• Coxsackie virus
• Rubella virus
• Epstein-Barr virus
• Varicella zoster virus 3

Fungal Causes (Uncommon):

• Blastomyces dermatitidis
• Histoplasma capsulatum
• Coccidioides immitis 3

Mycobacterial Causes:

• Mycobacterium tuberculosis (genitourinary TB) 3
• Mycobacterium bovis (particularly following intravesical BCG therapy for bladder cancer) 4

Clinical Context and Pathophysiology

The infection typically occurs through retrograde migration of pathogens from the urethra or bladder in up to 90% of cases 5. In your 31-year-old patient, the sexually transmitted route is most likely, with organisms ascending through the vas deferens to reach the epididymis.

Important Clinical Pitfall:

Research demonstrates that only 50.1% of men diagnosed with epididymo-orchitis are actually tested for gonorrhea and chlamydia, yet among those tested, 13.8% are positive 6. Among men <35 years, chlamydia (12.3%) is more common than gonorrhea (3.1%) 6. This represents a significant gap in appropriate diagnostic workup that can lead to inadequate treatment and continued transmission.

Diagnostic Algorithm for Your 31-Year-Old Patient

Given the age-specific etiology, the following should be obtained:

1. Urethral Gram stain or intraurethral swab for urethritis (>5 polymorphonuclear leukocytes per oil immersion field) 1
2. Nucleic acid amplification test (NAAT) on intraurethral swab or first-void urine for N. gonorrhoeae and C. trachomatis 1, 3
3. First-void urine examination for leukocytes if urethral Gram stain is negative, with culture and Gram stain 1
4. Syphilis serology and HIV testing 1

Critical Distinction:

While the 2018 IDSA/ASM guideline 3 confirms that NAATs are the most sensitive diagnostic procedure for C. trachomatis and N. gonorrhoeae, culture of gonorrhea should be obtained when antibiotic resistance is a concern, requiring special media for antimicrobial susceptibility testing.

Summary of Pathogen Distribution by Age

For your 31-year-old patient, assume sexually transmitted pathogens first, with empiric treatment covering both C. trachomatis and N. gonorrhoeae before culture results are available 1, 2, 1. The most recent European guideline from 2024 5, 7 emphasizes that the predominant pathogens are Enterobacterales, C. trachomatis, and N. gonorrhoeae, with appropriate diagnostics identifying the causative organism in up to 90% of cases.