What is the most common cause of epididymal orchitis in a 12-month-old boy presenting with testicular pain and no evidence of testicular torsion on ultrasound?

Most Common Cause of Epididymo-Orchitis in a 12-Month-Old

In a 12-month-old boy with epididymo-orchitis and no torsion on ultrasound, the most common cause is retrograde spread of coliform bacteria (particularly E. coli) from the urinary tract, often associated with an underlying urinary tract abnormality.

Age-Specific Etiology

The etiology of epididymo-orchitis is highly age-dependent, and a 12-month-old falls into the prepubertal category where the pathophysiology differs markedly from adolescents and adults:

Prepubertal Children (<35 years but specifically infants/young children)

• Coliform bacteria, especially E. coli, are the primary pathogens in prepubertal children and adults over 35 years 1, 2, 3
• These represent "commonplace genitourinary infections" that reach the epididymis through retrograde propagation via the vas deferens 1
• Underlying urinary tract abnormalities are frequently present, most notably obstruction of the distal urinary tract 1
• E. coli was identified as the most common bacteria in urine cultures of patients with epididymo-orchitis across age groups 4

Contrast with Other Age Groups (Not Applicable Here)

• Sexually transmitted infections (Chlamydia trachomatis and Neisseria gonorrhoeae) are the predominant causes between puberty and 35 years of age 1, 2, 3
• This is clearly not relevant for a 12-month-old infant 5, 3

Mechanism of Infection

• Retrograde ascent of pathogens through the vas deferens is the usual route of epididymal infection 1, 2
• In this age group, the infection typically originates from the urinary tract rather than sexually transmitted sources 1, 3

Critical Clinical Considerations

Evaluate for Underlying Urological Abnormalities

• A urinary tract abnormality, particularly bladder outflow obstruction, is often the underlying cause in prepubertal children with epididymitis 1
• This infant requires evaluation for congenital urological anomalies that may predispose to urinary tract infections 1

Diagnostic Workup

• Urinalysis and urine culture are essential to identify the causative organism and guide antibiotic therapy 3, 4
• Approximately 20% of patients with epididymo-orchitis will have positive urine cultures growing bacteria at ≥10,000 CFU/ml 4
• Higher urine white blood cells, more urine bacteria, positive leukocyte esterase, and positive nitrites support bacterial urinary tract infection 4

Common Pitfall to Avoid

• Do not empirically treat for sexually transmitted infections in this age group - the pathogens and treatment approach differ completely from adolescents and young adults 1, 3
• Testing for gonorrhea and chlamydia is not indicated in a 12-month-old with epididymo-orchitis 3, 4

Treatment Approach

• Empiric antibiotic therapy should target coliform bacteria (enterobacteria) rather than sexually transmitted pathogens 1, 3
• For moderate symptoms, oral therapy with cotrimoxazole or second-generation quinolones can be used 1
• Severe disease requires admission for parenteral therapy with an aminoglycoside and cephalosporin combination, followed by oral antibiotics 1
• Antibiotics should be adjusted based on culture and sensitivity results 1