What causes parotitis?

What Causes Parotitis

Parotitis is most commonly caused by mumps virus in unvaccinated populations, but in vaccinated populations, bacterial infections (particularly Staphylococcus aureus and anaerobes), other viruses (Epstein-Barr virus, influenza, parainfluenza), and non-infectious causes (Sjögren syndrome, medications causing hyposalivation) predominate. 1, 2, 3

Viral Causes

Mumps Virus

• Mumps virus remains the most common viral cause of parotitis globally, though its incidence has dramatically decreased in vaccinated populations 1, 4, 3
• Only 30-40% of mumps infections produce typical acute parotitis; 15-20% are asymptomatic 1, 5
• Parotitis typically develops 16-18 days after mumps exposure, often preceded by fever, headache, malaise, myalgia, and anorexia 1, 5
• Despite high MMR vaccine effectiveness (~88%), breakthrough infections still occur, particularly during outbreaks 6, 5

Other Viruses

• Epstein-Barr virus is a recognized viral cause of parotitis 3
• Influenza A virus can cause acute parotitis, confirmed by subtyped influenza A testing 7, 3
• Parainfluenza viruses are documented causes 3
• Coxsackievirus has been identified as a causative agent 3

Bacterial Causes

Acute Suppurative Parotitis

• Staphylococcus aureus is the most common bacterial pathogen causing acute suppurative parotitis 2, 3
• Anaerobic bacteria are increasingly recognized as important causes, including:
  • Gram-negative bacilli (pigmented Prevotella and Porphyromonas species) 2
  • Fusobacterium species 2
  • Peptostreptococcus species 2, 3
• Beta-lactamase-producing organisms can be isolated in almost three-fourths of patients 3
• Streptococcus species (including S. pneumoniae) are common bacterial causes 2
• Gram-negative bacilli (E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa) are often seen in hospitalized patients 2

Predisposing Factors for Bacterial Parotitis

• Dehydration and hyposalivation are major risk factors 2, 3
• Malnutrition increases susceptibility 3
• Medications that diminish salivation predispose to infection 3
• Oral neoplasms and immunosuppression are contributing factors 3
• Sialolithiasis (salivary stones) can lead to ascending infection 3
• Sjögren syndrome patients have increased risk due to chronic hyposalivation 1

Recurrent Parotitis

• Recurrent parotitis is probably caused by congenital abnormalities of salivary gland ducts with recurrent ascending infections, possibly aided by dehydration 8
• The parotid gland is predominantly affected due to its lower secretion rate compared to the submandibular gland 8
• This condition mainly affects children aged 3-6 years, with males more commonly affected, peaking in the first year of school 8

Non-Infectious Causes

• Sjögren syndrome may present with recurrent parotitis 1
• Immune-related adverse events from checkpoint inhibitors can cause parotitis 1
• Medications causing hyposalivation indirectly lead to bacterial parotitis 1, 3

Important Clinical Pitfall

In the post-MMR vaccine era, clinicians must not assume all parotitis is mumps. 7 Bacterial causes now predominate in many settings, and failure to recognize suppurative parotitis can lead to abscess formation requiring surgical drainage. 2, 3 Always consider the patient's vaccination status, clinical presentation (unilateral vs bilateral, presence of purulence), and risk factors for bacterial infection when determining etiology. 1, 3