What Causes Otitis Externa in Children
Otitis externa in children is nearly always (98%) a bacterial infection caused primarily by Pseudomonas aeruginosa (20-60% of cases) and Staphylococcus aureus (10-70% of cases), often occurring as a polymicrobial infection. 1
Primary Bacterial Pathogens
- Pseudomonas aeruginosa is the most frequently isolated organism, accounting for 20-60% of cases in children with otitis externa 1, 2
- Staphylococcus aureus is the second most common pathogen, responsible for 10-70% of infections 1, 2
- Other gram-negative organisms (excluding P. aeruginosa) collectively cause only 2-3% of cases 1
- Methicillin-resistant Staphylococcus aureus (MRSA) should be suspected when otorrhea is recurrent or fails to respond to initial treatment 1
Fungal Causes (Less Common)
- Fungal infections are distinctly uncommon in primary acute otitis externa but may occur after prolonged topical antibiotic therapy 1
- Aspergillus and Candida species are the primary fungal pathogens when otomycosis does occur 1, 2
- Fungal overgrowth is more likely in tropical climates, humid environments, diabetic patients, or immunocompromised children 3
Predisposing Environmental and Mechanical Factors
The infection develops when the ear canal's natural protective mechanisms are disrupted:
- Excessive moisture exposure (hence "swimmer's ear") converts the normal acidic pH of the external auditory canal to an alkaline environment, promoting bacterial growth 1
- Trauma to the ear canal from cotton swabs, fingernails, or other objects disrupts the protective epithelial barrier 4, 5
- Water activities are strongly associated with otitis externa, with 44% of visits occurring during summer months (June-August) 1
- Warm, humid climates increase susceptibility, with the highest incidence in the Southern United States (9.1 per 1000 population) 1
Age-Related Epidemiology
- Children aged 5-14 years account for just under half of all otitis externa visits 1
- The condition is uncommon before age 2 years, with very limited evidence for this age group 1
- Lifetime incidence reaches approximately 10% across all ages 1, 2
Important Clinical Caveat
Otitis externa must be distinguished from acute otitis media in children, as the latter is caused by different organisms (Streptococcus pneumoniae and Hemophilus influenzae) and requires different management 1. The hallmark differentiating feature is intense tenderness with manipulation of the tragus or pinna in otitis externa, which is absent in otitis media 1, 3.