In an older adult with acute unilateral painful parotid swelling, how can bacterial parotitis be distinguished from viral parotitis?

Distinguishing Bacterial from Viral Parotitis in Older Adults

In an older adult with acute unilateral painful parotid swelling, bacterial parotitis is distinguished from viral parotitis by the presence of purulent discharge from Stensen's duct, severe systemic toxicity with high fever, and predisposing risk factors such as dehydration or recent hospitalization—whereas viral parotitis typically presents with bilateral involvement, milder constitutional symptoms, and absence of purulent drainage. 1

Key Clinical Features That Favor Bacterial Parotitis

Purulent Discharge from Stensen's Duct

• Bacterial parotitis characteristically produces purulent discharge from the parotid duct opening (Stensen's duct) into the oral cavity, which can be expressed by massaging the gland; this finding is highly specific for bacterial infection and is absent in viral parotitis. 2, 1
• The presence of pus expressible from the duct is the single most reliable clinical sign differentiating bacterial from viral etiology. 1

Unilateral vs. Bilateral Involvement

• Bacterial parotitis is unilateral in approximately 83% of cases, whereas viral parotitis (including mumps and other viral causes) typically presents with bilateral parotid swelling. 2, 1
• Unilateral painful parotid swelling in an older adult should raise immediate suspicion for bacterial infection. 2

Severity of Systemic Symptoms

• Bacterial parotitis presents with severe systemic toxicity including high fever, marked tenderness, overlying skin erythema, and rapid progression, whereas viral parotitis causes milder constitutional symptoms with gradual onset. 1, 3
• The affected gland in bacterial parotitis is exquisitely tender, firm, and warm to touch with overlying skin changes—features uncommon in viral disease. 1

Predisposing Risk Factors

• Bacterial parotitis occurs almost exclusively in patients with identifiable risk factors: dehydration, malnutrition, recent hospitalization, immunosuppression, medications that reduce salivation (anticholinergics, diuretics), sialolithiasis, or oral neoplasms. 1, 3
• Viral parotitis occurs in otherwise healthy individuals without these predisposing conditions. 4

Laboratory and Imaging Findings

Serum Amylase

• Serum amylase levels are generally NOT elevated in bacterial parotitis despite marked parotid swelling (67% of cases show normal amylase), whereas viral parotitis may cause mild elevation. 2
• This counterintuitive finding helps distinguish bacterial from viral etiology when combined with clinical features. 2

Imaging Characteristics

• Diffusion-weighted MRI in bacterial parotitis shows multiple punctate hyperintensities with reduced apparent diffusion coefficient, indicating microabscess formation—a pattern not seen in viral parotitis. 2
• Contrast-enhanced CT or MRI may demonstrate abscess formation, ductal dilatation, or surrounding cellulitis in bacterial cases. 2

Microbiologic Diagnosis

• Pus aspirated from the gland or expressed from Stensen's duct should be cultured on media supporting aerobic and anaerobic bacteria; the most common pathogens are Staphylococcus aureus (65% of cases, including 19% MRSA) and anaerobes (Peptostreptococcus, Prevotella, Porphyromonas species). 2, 1, 3
• Gram-negative organisms (E. coli, Klebsiella, Pseudomonas) are frequently isolated in hospitalized or debilitated patients. 3
• Beta-lactamase-producing organisms are recovered in approximately 75% of bacterial parotitis cases. 1

Key Features That Favor Viral Parotitis

Bilateral Involvement and Milder Course

• Viral parotitis typically presents with bilateral parotid swelling (though unilateral cases occur), gradual onset over 1-2 days, and spontaneous resolution within 7-10 days without antibiotics. 4
• Constitutional symptoms are milder, and the gland is less tender with no overlying skin changes. 4

Absence of Purulent Discharge

• No purulent material can be expressed from Stensen's duct in viral parotitis; the duct opening appears normal without inflammation. 1, 4

Viral Etiologies to Consider

• Influenza A (particularly H3N2), human herpesvirus 6B (HHV6B), and Epstein-Barr virus (EBV) are the most common non-mumps viral causes of parotitis in adults, especially during influenza season. 4
• Mumps remains a consideration in unvaccinated individuals or during outbreaks, though it is now rare in vaccinated populations. 4
• Other viral causes include parainfluenza viruses (HPIV 1-4), adenovirus, coxsackievirus, cytomegalovirus, and herpes simplex viruses. 1, 4

Epidemiologic Context

• Viral parotitis often occurs during respiratory virus season (fall/winter) and may be associated with concurrent upper respiratory symptoms such as sore throat (55% of cases) and cough. 4
• Patients lack the predisposing risk factors seen in bacterial parotitis. 4

Diagnostic Algorithm

Step 1: Assess for Purulent Discharge

• Examine the opening of Stensen's duct (opposite the upper second molar) and gently massage the parotid gland; expressible pus confirms bacterial infection. 1

Step 2: Evaluate Laterality and Severity

• Unilateral involvement + severe tenderness + skin erythema → bacterial parotitis. 2, 1
• Bilateral involvement + milder symptoms + no skin changes → viral parotitis. 4

Step 3: Identify Risk Factors

• Presence of dehydration, recent hospitalization, immunosuppression, or salivary-reducing medications → bacterial parotitis. 1, 3
• Otherwise healthy patient during viral season → viral parotitis. 4

Step 4: Laboratory Testing

• Obtain buccal swab or aspirate for bacterial culture (aerobic and anaerobic) if bacterial parotitis is suspected; also send for viral PCR panel (influenza, EBV, HHV6B) if viral etiology is considered. 1, 3, 4
• Check serum amylase (usually normal in bacterial parotitis). 2

Step 5: Imaging When Indicated

• Order contrast-enhanced CT or MRI if abscess formation is suspected (fluctuance, failure to improve with antibiotics, or severe systemic toxicity). 2
• Diffusion-weighted MRI can detect early microabscess formation before frank pus accumulates. 2

Management Implications

Bacterial Parotitis

• Initiate empiric parenteral antibiotics covering S. aureus (including MRSA) and anaerobes: vancomycin plus piperacillin-tazobactam or ampicillin-sulbactam. 1, 3
• Ensure adequate hydration and consider sialagogues (lemon drops, massage) to promote salivary flow. 1, 3
• Surgical drainage is required once abscess formation occurs; failure to drain can lead to complications including facial nerve injury, osteomyelitis, or sepsis. 1, 3

Viral Parotitis

• Provide supportive care only: analgesics, hydration, warm compresses, and reassurance of self-limited course. 4
• No antibiotics are indicated for viral parotitis; inappropriate antibiotic use contributes to resistance without clinical benefit. 4

Critical Pitfalls to Avoid

• Do not assume bilateral swelling rules out bacterial infection; 17% of bacterial parotitis cases are bilateral. 2
• Do not rely on serum amylase to distinguish bacterial from viral parotitis; amylase is typically normal in bacterial cases despite severe gland inflammation. 2
• Do not delay surgical consultation when abscess is suspected; early drainage prevents complications and facilitates recovery. 1, 3
• Do not prescribe antibiotics for viral parotitis; this exposes patients to unnecessary adverse effects and promotes resistance. 4