What is the cause of bilateral parotid swelling in an unvaccinated child?

Bilateral Parotid Swelling in an Unvaccinated Child: Mumps

The most likely cause of bilateral parotid swelling in an unvaccinated child is mumps, a vaccine-preventable viral illness that classically presents with acute onset of tender parotid gland swelling lasting ≥2 days. 1, 2

Clinical Diagnosis

The Advisory Committee on Immunization Practices defines mumps 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, 2 In this unvaccinated child, mumps should be at the top of your differential diagnosis given:

• Classic bilateral parotid involvement is the hallmark presentation, though unilateral swelling occurs less commonly 2, 3
• Prodromal symptoms typically precede parotitis by 16-18 days after exposure and include fever, headache, malaise, myalgia, and anorexia 2, 4
• Age predilection: Parotitis occurs most commonly in children aged 2-9 years 2

Critical Diagnostic Caveat

Do not rely solely on clinical diagnosis—laboratory confirmation is strongly preferred because parotitis has multiple other causes and mumps presentation is highly variable. 2 Importantly:

• Only 30-40% of mumps infections produce typical acute parotitis 5, 2
• 15-20% of infections are completely asymptomatic 5, 2
• Up to 50% present with nonspecific respiratory symptoms without classic parotid involvement 5, 2
• One study found one-third of clinically diagnosed mumps cases had no serologic evidence of actual mumps infection 1, 2

Laboratory Confirmation

Obtain laboratory confirmation through: 1, 2

• Isolation of mumps virus from clinical specimens (saliva, buccal swab from parotid duct), OR
• Significant rise in serum mumps IgG antibody between acute and convalescent phases, OR
• Positive mumps IgM antibody testing

Immediate Management Steps

Implement droplet precautions immediately as patients are contagious from 7 days before through 8 days after parotitis onset. 5 Isolate the child for 5 days after onset of parotitis to limit spread to susceptible contacts. 5

Report the case immediately to state and local health departments as mumps is a reportable disease. 1

Symptomatic Treatment

• Provide acetaminophen or NSAIDs for pain and fever control 5
• Ensure adequate hydration and fluid intake, as parotitis makes swallowing uncomfortable 5
• Recommend soft foods and avoidance of acidic foods that stimulate salivary flow and worsen parotid pain 5

Monitor for Complications

Neurological complications to watch for include: 5

• Aseptic meningitis (4-6% of cases): severe headache, neck stiffness, photophobia, altered mental status
• Encephalitis: seizures, paralysis, cranial nerve palsies
• Hearing loss, including sudden sensorineural deafness (historically a major cause of childhood deafness pre-vaccine era)

Other complications include pancreatitis (severe abdominal pain, nausea, vomiting) and, if postpubertal, orchitis in males or oophoritis in females. 5, 3

Alternative Diagnoses to Consider

While mumps is most likely in this unvaccinated child with bilateral parotid swelling, other causes of parotitis include:

• Bacterial parotitis (typically unilateral, purulent discharge from Stensen's duct, more acute presentation)
• Other viral causes: Epstein-Barr virus, cytomegalovirus, HIV
• Non-infectious causes: Sialolithiasis, autoimmune conditions (Sjögren's syndrome), drug reactions

The bilateral presentation, vaccination status, and typical age range make mumps the primary diagnosis to confirm. 2, 3