A 5-year-old boy presents with bilateral parotid swelling, fever, and difficulty eating for 2 days. He has no history of MMR vaccination. The parents report that a classmate had similar symptoms 1 week ago. What is the most appropriate investigation to confirm mumps?

Explanation

## Diagnostic Confirmation of Mumps ### Clinical Presentation The patient has **bilateral parotitis**, fever, and dysphagia — classic mumps presentation. The epidemiological link (classmate with similar illness 1 week prior) supports mumps in an unvaccinated child. Laboratory confirmation is required to differentiate from other causes of parotitis (bacterial, other viral, autoimmune). ### Investigation Comparison | Investigation | Specimen | Timing | Sensitivity | Specificity | Clinical Use | |---|---|---|---|---|---| | **RT-PCR (saliva/buccal)** | Saliva or buccal swab | First 3–5 days | 95–98% | 99–100% | **Gold standard; earliest detection** | | Viral culture (saliva) | Saliva | First 3–5 days | 60–70% | 100% | Slower; less sensitive than RT-PCR | | Mumps IgM serum | Serum | Day 3–4 onwards | 85–90% | 95% | Appears after symptom onset | | Serum amylase | Serum | Acute phase | Low specificity | Low specificity | Supports diagnosis but not confirmatory | ### Why RT-PCR Is Optimal **Key Point:** RT-PCR from saliva or buccal swab is the **investigation of choice** for mumps confirmation because it detects viral RNA with highest sensitivity during the acute phase (first 3–5 days) when viral shedding is maximal. **High-Yield:** Mumps virus is present in **saliva and respiratory secretions** from 2 days before parotitis onset through 5 days after onset. This is the optimal window for molecular detection. **Clinical Pearl:** Mumps IgM becomes positive around day 3–4 of illness; if tested too early (within 48 hours), it may be falsely negative. RT-PCR is therefore more reliable for **early acute diagnosis**. ### Specimen Collection - Saliva (preferred) or buccal swab - Collect within first 3–5 days of parotitis onset - Transport at 2–8°C; do not freeze if RT-PCR is planned **Mnemonic: MUMPS DIAGNOSIS WINDOW** - **M**olecular (RT-PCR): Days 1–5 (best) - **U**nder 48 hours: IgM may be negative - **M**aximal shedding: Saliva (first 5 days) - **P**ancreatic enzyme: Amylase ↑ but non-specific - **S**erology: IgM from day 3–4 onwards [cite:Park 26e Ch 8]