What causes unilateral parotitis or mastoiditis?

Causes of Unilateral Parotitis and Mastoiditis

Unilateral Parotitis

Acute bacterial suppurative parotitis is most commonly caused by Staphylococcus aureus and anaerobic bacteria, with gram-negative organisms frequently seen in hospitalized patients. 1

Primary Bacterial Pathogens

• Staphylococcus aureus is the predominant aerobic pathogen in acute bacterial parotitis 1
• Anaerobic bacteria are equally common, including:
  • Pigmented Prevotella and Porphyromonas species 1
  • Fusobacterium species 1
  • Peptostreptococcus species 1

Secondary Pathogens

• Streptococcus pneumoniae can cause acute suppurative parotitis, particularly in immunocompromised patients (HIV-infected individuals should be suspected in cases of invasive pneumococcal parotitis) 2
• Gram-negative bacilli including Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa are more common in hospitalized patients 1
• Streptococcus species (non-pneumoniae) 1

Rare Causes

• Haemophilus influenzae, Salmonella species, Treponema pallidum, cat-scratch bacillus, Eikenella corrodens, Mycobacterium tuberculosis, and atypical mycobacteria 1

Underlying Mechanism

Parotitis typically results from decreased salivary flow or ductal obstruction, leading to ascending infection from the oral cavity 3, 4

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Mastoiditis

Acute mastoiditis is caused primarily by Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, and Haemophilus influenzae, representing a complication of acute otitis media. 5, 6

Acute Mastoiditis Pathogens

• Streptococcus pneumoniae remains the most common pathogen (28.57% of culture-positive cases) 3, 6
• Staphylococcus aureus shows a significantly high rate (16.32% of cases) and is increasing in frequency 6
• Streptococcus pyogenes causes more severe inflammation and higher rates of spontaneous tympanic membrane rupture and progression to acute mastoiditis 3
• Haemophilus influenzae has become nearly equal in frequency to S. pneumoniae following PCV7 vaccination 3

Chronic Mastoiditis Pathogens

• Pseudomonas aeruginosa predominates in chronic cases, though contamination from the ear canal must be considered 5
• Anaerobic bacteria are the most common isolates when adequate isolation methods are employed 5
• Enterobacteriaceae and S. aureus 5

Important Clinical Context

• Culture-negative cases occur in 53.68% of mastoiditis cases, likely due to prior antibiotic therapy 6
• Prior antibiotic treatment does not prevent mastoiditis development, with 33-81% of patients having received antibiotics before diagnosis 7, 8, 6
• The incidence has doubled since 1999, with increasing surgical intervention rates (from 4.3% to 33%, reaching 70% in 2005) 6

Mechanism of Development

Mastoiditis develops as the most common intratemporal complication of acute otitis media, with direct extension of infection from the middle ear into the mastoid air cells 5, 7