What causes recurrent ear infections?

Causes of Recurrent Ear Infections

Recurrent ear infections result from a combination of viral upper respiratory tract infections that compromise eustachian tube function, followed by bacterial colonization with Streptococcus pneumoniae, non-typeable Haemophilus influenzae, and Moraxella catarrhalis. 1

Primary Infectious Pathway

The fundamental mechanism begins with viral infection:

• Viral upper respiratory tract infections (URTIs) always precede acute otitis media (AOM), causing inflammation of the nasopharyngeal and eustachian tube epithelium 1
• This viral infection leads to eustachian tube dysfunction, creating negative middle ear pressure and allowing secretions containing both viruses and bacteria from the nasopharynx to enter the middle ear 1
• Bacteria and/or viruses can be detected in middle ear fluid in up to 96% of AOM cases (66% bacteria and viruses together, 27% bacteria alone, 4% virus alone) 1

Bacterial Pathogens

The three dominant bacterial causes have evolved over time:

• Streptococcus pneumoniae, non-typeable Haemophilus influenzae, and Moraxella catarrhalis are the most common bacterial pathogens 1, 2
• Since introduction of pneumococcal conjugate vaccines (PCV7 in 2000, later PCV13), the distribution has shifted with H. influenzae becoming more prominent and non-vaccine serotypes of S. pneumoniae emerging 1
• Streptococcus pyogenes accounts for less than 5% of cases 1

Eustachian Tube Dysfunction

Poor eustachian tube function is the underlying anatomic predisposition:

• Eustachian tube dysfunction underlies most cases of otitis media, preventing proper middle ear ventilation and drainage 1, 3
• This dysfunction is particularly common in young children due to anatomic factors 1
• The eustachian tube connects the middle ear to the nasopharynx, and when it fails to function properly, fluid accumulates and becomes infected 1

Biofilm Formation

Persistent bacterial colonization contributes to recurrence:

• Bacterial biofilms have been demonstrated in middle ears of patients with chronic and recurrent infections, protecting bacteria against antibiotics and immune responses 1
• These biofilms form on middle ear mucosa and in middle ear effusion, making infections more difficult to eradicate 1

Age-Related Risk Factors

Peak incidence occurs in early childhood:

• The highest rates of AOM occur in children 1-4 years of age (61 new episodes per 100 children per year) 4
• By age 3, the majority of children will have experienced at least one AOM episode 4
• This age vulnerability relates to immature immune systems and eustachian tube anatomy 1

Environmental and Host Factors

Multiple additional factors increase susceptibility:

• Day care attendance, older siblings, and passive smoke exposure increase infection frequency 1
• Adenoid hypertrophy can contribute to recurrent infections by obstructing the eustachian tube 1
• Allergic inflammation predisposes to bacterial superinfection 1

Immunologic Considerations

In cases of unusually severe or frequent infections:

• Primary immunodeficiency disorders should be considered when infections are repetitive, severe, or refractory to therapy 1
• Up to 26% of children older than 2 years with invasive pneumococcal disease have an identifiable primary immunodeficiency 1

Common Pitfall

Do not confuse otitis media with effusion (OME) with acute otitis media (AOM) - OME presents without acute infectious symptoms and does not require antibiotics, while AOM requires rapid onset, middle ear effusion, and signs of inflammation 4, 2. This distinction is critical as misdiagnosis leads to unnecessary antibiotic prescriptions 4.

When to Investigate Further

If otorrhea persists after full treatment or if two or more episodes occur within six months, further evaluation is recommended to exclude underlying conditions such as cholesteatoma, foreign body, or tumor 5.