What is the recommended approach for testing and managing a patient with suspected mumps, considering their vaccination history and potential for complications?

Mumps Testing and Diagnosis

Laboratory confirmation is essential for all suspected mumps cases, as clinical diagnosis alone is unreliable—with approximately one-third of clinically diagnosed cases lacking serologic evidence of actual mumps infection. 1, 2

Clinical Case Definition

A clinical case of mumps requires:

• Acute onset of unilateral or bilateral tender, self-limited parotid or salivary gland swelling lasting ≥2 days without other apparent cause 1
• However, parotitis has multiple infectious and noninfectious causes (EBV, CMV, HIV, bacterial infections), making laboratory confirmation mandatory 1, 2

Laboratory Testing Algorithm

First-Line Testing (Highest Diagnostic Yield)

Buccal/parotid duct swab RT-PCR is the single most sensitive test, with 90% positivity in confirmed cases versus only 43% for IgM serology. 3

• Collect buccal swab RT-PCR within 9 days of symptom onset (ideally within 1 day) 4, 3
• This is particularly critical in vaccinated patients, where IgM sensitivity drops to only 34% compared to 64% in unvaccinated patients 3
• Urine RT-PCR can be collected as an adjunct, remaining positive for at least 5 days after oral detection 4

Laboratory Confirmation Criteria

A confirmed case requires one of the following: 1

• Isolation of mumps virus from clinical specimen (buccal swab, urine), OR
• Positive mumps IgM antibody, OR
• Significant rise in acute and convalescent mumps IgG titers (requires paired sera 2-3 weeks apart)

Critical Testing Pitfalls in Vaccinated Populations

In highly vaccinated populations (which now constitute 85% of mumps cases), serological IgM testing has severely limited sensitivity and should never be used alone. 5, 6

• IgM positivity was only 45% in one outbreak among vaccinated patients, while RT-PCR was 83% positive 5
• Always confirm negative or equivocal IgM results with RT-PCR testing 5
• Vaccination status inversely correlates with IgM detection rates 3

Specimen Collection Timing

Timing of specimen collection is critical for diagnostic yield: 3

• Buccal swabs: Collect within 1 day of symptom onset for optimal sensitivity
• Urine specimens: Collect within 2 days of symptom onset
• IgM serology: Most reliable 3-5 days after symptom onset, but still inferior to RT-PCR in vaccinated patients 3

Mandatory Reporting and Contact Investigation

Report all probable or confirmed cases immediately to state and local health departments. 1, 7

Required follow-up actions include: 1

• Identification of all contacts
• Follow-up of susceptible contacts
• Serologic/RT-PCR testing of all probable cases to confirm diagnosis
• Active surveillance for two incubation periods (5-6 weeks) after the last case 1, 7

Additional Testing Considerations

Test all patients with parotitis for HIV, regardless of apparent risk factors, as HIV can present with parotid swelling during acute seroconversion or chronic disease. 2, 4

Consider testing for other viral causes (EBV, CMV, enteroviruses, influenza A, parainfluenza) if mumps testing is negative, particularly in immunocompromised patients. 2

Vaccination History Assessment

Document vaccination status for all cases: 6

• Number of previous MMR doses (0,1, or 2)
• Vaccination status correlates with disease severity and complication rates
• Two MMR doses provide 62.7% effectiveness against complications versus 52.1% for one dose 6

Outbreak-Specific Genotyping

Viral genotyping through SH gene sequencing allows epidemiologic linkage of geographically distinct cases and confirms outbreak relatedness. 3

• Most recent North American outbreaks involve genotype G strains 5, 3
• Genotyping is performed by state health department or CDC reference laboratories 1