What are the diagnostic criteria and management options for a patient presenting with symptoms of mumps, considering their vaccination history, exposure to others, and potential complications?

Diagnosis of Mumps

Mumps diagnosis requires laboratory confirmation in addition to clinical criteria, as clinical diagnosis alone misidentifies one-third of cases, and you should prioritize buccal swab RT-PCR over serology, especially in vaccinated patients. 1, 2

Clinical Diagnostic Criteria

A clinical case of mumps is defined as acute onset of unilateral or bilateral tender, self-limited swelling of the parotid or other salivary gland lasting ≥2 days without other apparent cause. 1

Key Clinical Features to Document:

• Duration of parotid/salivary gland swelling must be ≥2 days 1
• Tenderness of the affected gland(s) 1
• Absence of purulent discharge from Stensen's duct (which would suggest bacterial sialadenitis instead) 3
• Bilateral involvement is characteristic but not required 1, 4

Critical Pitfall to Avoid:

Do not rely on clinical diagnosis alone—parotitis has multiple infectious and noninfectious causes, and one-third of clinically diagnosed mumps cases lack serologic evidence of actual mumps infection. 1, 5 Vaccination history does not rule out mumps, as vaccine efficacy ranges only 75-95%, and recent outbreaks have occurred predominantly in vaccinated populations. 6, 4

Laboratory Confirmation (Essential for All Cases)

Preferred Diagnostic Approach:

Order buccal swab RT-PCR as your first-line test—it has 90% positivity in confirmed cases compared to only 43% for both IgM serology and urine RT-PCR. 2

Specimen Collection Timing:

• Collect buccal swabs within 9 days of symptom onset (typically collected 1 day after onset) 3, 2
• Massage the parotid gland for 30 seconds before obtaining the parotid duct swab 3
• Urine PCR remains positive for at least 5 days but is less sensitive than buccal specimens 3

Laboratory Criteria for Confirmation:

The CDC defines laboratory-confirmed mumps as meeting one of the following: 1

1. Isolation of mumps virus from clinical specimen 1
2. Positive mumps IgM antibody 1
3. Significant rise between acute and convalescent-phase titers in serum mumps IgG antibody 1

Critical Limitation of Serology in Vaccinated Patients:

Mumps IgM detection is significantly lower in vaccinated patients (34%) compared to unvaccinated patients (64%), making RT-PCR essential in vaccinated populations. 2 In outbreak settings among highly vaccinated populations, only 45% had positive or equivocal IgM at first sampling, whereas 83% had positive RT-PCR. 7

Case Classification Algorithm

Confirmed Case:

• Meets laboratory criteria (RT-PCR positive, IgM positive, or significant IgG rise), OR 1
• Meets clinical case definition AND is epidemiologically linked to a confirmed or probable case 1
• Two probable cases that are epidemiologically linked are considered confirmed even without laboratory confirmation 1

Probable Case:

• Meets clinical case definition 1
• NOT epidemiologically linked to confirmed/probable case 1
• Has noncontributory or no serologic/virologic testing 1

Differential Diagnoses to Exclude

Infectious Causes:

• Bacterial sialadenitis: Look for unilateral swelling, purulent discharge from Stensen's duct, fever, and predisposing factors like dehydration 3
• Other viral parotitis: EBV, CMV, HIV, influenza A, parainfluenza, adenovirus, enteroviruses 5
• HIV: Test all patients with parotitis for HIV regardless of apparent risk factors, as HIV can present with parotid swelling 3, 5

Key Distinguishing Feature from Measles:

Mumps does not produce the generalized maculopapular rash lasting ≥3 days or the "three Cs" (cough, coryza, conjunctivitis) characteristic of measles. 6

Management Considerations

Immediate Actions:

• Report probable or confirmed cases immediately to state and local health departments 1
• Implement droplet precautions and isolation for 5 days after parotitis onset 3
• Identify all contacts and follow up susceptible contacts 1

Vaccination History Assessment:

• Document MMR vaccination doses—lack of vaccination or birth after 1957 without documented immunity increases risk 3
• Remember that mumps can occur in highly vaccinated populations, so vaccination history does not exclude diagnosis 6, 4

Complications to Monitor:

Watch for orchitis in adolescent/adult males, aseptic meningitis, encephalitis, oophoritis in adult females, deafness, and pancreatitis—these complications occur more frequently in adults than children. 4, 8