How to differentiate between bacterial and viral orchitis through physical examination and history taking?

Differentiating Bacterial from Viral Orchitis Through History and Physical Examination

The key to distinguishing bacterial from viral orchitis lies in age-based pathogen patterns, associated symptoms, and onset characteristics: men under 35 with gradual onset, urethral discharge, and dysuria likely have bacterial orchitis from sexually transmitted pathogens, while concurrent parotitis or known mumps exposure strongly suggests viral orchitis. 1

Age-Based Clinical Patterns

Men Under 35 Years

• Bacterial orchitis in this age group is predominantly caused by sexually transmitted pathogens (Chlamydia trachomatis and Neisseria gonorrhoeae), presenting with gradual onset and concurrent urinary tract symptoms 1, 2, 3
• These patients typically have urethritis symptoms: urethral discharge, dysuria, and frequency 4, 5
• The inflammation usually begins as epididymitis that extends to the testis (epididymo-orchitis), with swelling starting at the lower pole of the epididymis and progressing upward 5, 6
• Sexual history revealing multiple partners, new partners, or partners with STI symptoms supports bacterial etiology 1

Men 35 Years and Older

• Bacterial orchitis in older men is typically caused by gram-negative enteric organisms (especially E. coli) and gram-positive bacteria 1, 2, 3
• These patients often have underlying urologic abnormalities: bladder outflow obstruction, benign prostatic hyperplasia, or recent urologic instrumentation 3, 5
• History of recent catheterization, cystoscopy, or other endourethral procedures points toward bacterial infection 3
• Concurrent lower urinary tract symptoms (frequency, urgency, hesitancy) suggest bacterial etiology 5

Viral Orchitis (All Ages)

• Mumps orchitis is the most common viral cause, occurring 4-7 days after parotitis in unvaccinated individuals 1, 4, 6
• History of recent mumps exposure or concurrent/recent parotid swelling is highly suggestive 1, 4
• Other viral causes include Coxsackie virus, rubella, Epstein-Barr virus, and varicella-zoster virus 4
• Viral orchitis typically presents with blood-borne dissemination rather than ascending infection 6

Physical Examination Findings

Distinguishing Features on Examination

Bacterial Orchitis:

• Epididymal involvement is prominent: swelling and tenderness begin at the lower pole of the epididymis and progress to the upper pole 5
• Urethral discharge may be visible on examination, particularly in younger men with STI-related disease 4, 5
• The cremasteric reflex is typically preserved (unlike testicular torsion) 5
• Palpable bladder or enlarged prostate on digital rectal examination suggests underlying urologic pathology in older men 5
• Gradual onset of swelling over hours to days 3, 5

Viral Orchitis:

• Isolated testicular involvement is more common, with less prominent epididymal swelling 6, 7
• Bilateral involvement occurs in approximately 30% of mumps orchitis cases 6
• Parotid gland swelling may be present or have recently resolved 1, 4
• Systemic viral symptoms: fever, malaise, myalgias without urinary symptoms 6, 7
• Testicular enlargement may be more diffuse and symmetric 7

Critical Physical Examination Steps

1. Inspect for urethral discharge: express the urethra from base to meatus to identify purulent discharge suggesting bacterial STI 4, 5
2. Palpate the epididymis separately from the testis: bacterial infection typically shows prominent epididymal tenderness and swelling starting at the tail 5
3. Examine the parotid glands: swelling or tenderness suggests mumps-related viral orchitis 1, 4
4. Assess for systemic signs: fever pattern (early in viral illness vs. persistent in bacterial), constitutional symptoms 3, 6
5. Perform abdominal and rectal examination in older men to identify urologic abnormalities 5

History-Taking Priorities

Essential Historical Elements

For Bacterial Orchitis:

• Sexual history: number of partners, new partners in past 60 days, partner symptoms, condom use 1, 4
• Urinary symptoms: dysuria, frequency, urgency, hesitancy, prior UTIs 3, 5
• Recent urologic procedures: catheterization, cystoscopy, prostate biopsy 3
• Onset pattern: gradual progression over days 3, 5

For Viral Orchitis:

• Vaccination history: mumps vaccination status 1, 4
• Recent viral illness: parotitis, upper respiratory infection, viral exanthem 4, 6
• Exposure history: contact with individuals with mumps or other viral illnesses 1
• Systemic symptoms: fever, malaise, myalgias without urinary complaints 6, 7

Common Pitfalls to Avoid

• Do not rely solely on fever presence: both bacterial and viral orchitis can present with fever, though timing differs (early in viral, persistent in bacterial) 3, 6
• Do not assume unilateral presentation excludes viral orchitis: while bilateral involvement suggests viral etiology, unilateral presentation occurs in 70% of mumps orchitis 6
• Do not overlook testicular torsion: if any suspicion exists based on sudden onset, absent cremasteric reflex, or high-riding testis, immediate surgical referral is mandatory 4, 5
• Do not assume age alone determines etiology: while age-based patterns exist, obtain appropriate testing before treatment 1, 2
• Do not forget to examine sexual partners: if bacterial STI is suspected, partners within 60 days require evaluation and presumptive treatment 4

Diagnostic Testing Algorithm Based on Clinical Suspicion

For suspected bacterial orchitis in men <35 years:

• Obtain nucleic acid amplification tests (NAATs) for C. trachomatis and N. gonorrhoeae from first-void urine or urethral swab 1, 4, 2
• Gram stain of urethral discharge if present 4

For suspected bacterial orchitis in men ≥35 years:

• Obtain midstream urine culture and urinalysis 1, 4
• Consider urethral culture if discharge is present 1

For suspected viral orchitis:

• Obtain mumps serology: IgM antibodies for acute infection or acute and convalescent IgG titers 1, 4
• Consider testing for other viral pathogens based on clinical presentation 4

Critical timing consideration:

• Obtain all cultures and NAATs before administering antibiotics to avoid false-negative results 1