What are the most common bacteria that cause otitis media?

Most Common Bacteria Causing Otitis Media

The three most common bacterial pathogens causing acute otitis media are Streptococcus pneumoniae, nontypeable Haemophilus influenzae, and Moraxella catarrhalis, with their relative prevalence shifting over time due to vaccination practices. 1

Bacterial Pathogens and Their Prevalence

Acute otitis media (AOM) is the most common reason for pediatric healthcare visits. When using appropriate diagnostic criteria and sensitive microbiologic techniques, bacteria can be detected in the middle ear fluid in up to 96% of AOM cases, often alongside viral pathogens. The main causative bacteria include:

1. Streptococcus pneumoniae

   • Historically was the most frequently isolated pathogen
   • Prevalence has fluctuated following pneumococcal conjugate vaccine (PCV) introduction
   • Non-vaccine serotypes have increased following vaccination

2. Nontypeable Haemophilus influenzae

   • Became the predominant pathogen shortly after PCV7 introduction
   • Currently nearly equal in prevalence to S. pneumoniae

3. Moraxella catarrhalis

   • Third most common bacterial cause

4. Less common pathogens:

   • Streptococcus pyogenes (Group A β-hemolytic streptococci) - accounts for less than 5% of AOM cases
   • Staphylococcus aureus - uncommon cause
   • Pseudomonas aeruginosa - rare, more common in chronic cases

Shifting Patterns in Bacterial Prevalence

The relative frequency of these pathogens has evolved over time, particularly following the introduction of pneumococcal vaccines:

• Pre-PCV7 era: S. pneumoniae was the predominant pathogen
• Early post-PCV7 era: H. influenzae became the most frequently isolated pathogen
• Later post-PCV7 era: Non-PCV7 serotypes of S. pneumoniae increased
• Current era: S. pneumoniae and H. influenzae are nearly equal in prevalence

Specific data from 2005-2009 showed fluctuating patterns 1:

• 2005-2006: 48% S. pneumoniae, 42% H. influenzae
• 2006-2007: Equal at 41% each
• 2007-2008: 35% S. pneumoniae, 59% H. influenzae
• 2008-2009: 54% S. pneumoniae, 38% H. influenzae

Clinical Implications

Understanding the bacterial etiology of AOM has important treatment implications:

• First-line treatment: High-dose amoxicillin (80-90 mg/kg/day divided in 2 doses) is effective against most S. pneumoniae strains 2
• Alternative treatment: For patients with recent amoxicillin use or treatment failure, amoxicillin-clavulanate provides better coverage against β-lactamase producing H. influenzae and M. catarrhalis 2
• Penicillin allergies: Cephalosporins (like cefdinir) for non-severe allergies; macrolides or TMP-SMX for severe allergies, though these have limited effectiveness against common otitis media pathogens 2

Diagnostic Considerations

Obtaining middle ear fluid for culture is not routinely performed in clinical practice and is reserved for:

• Treatment failures
• Immunocompromised patients
• Severely ill patients
• Research purposes

It's important to note that nasopharyngeal cultures do not accurately predict the causative agent of otitis media and should not be used for this purpose 1.

Key Pitfalls to Avoid

1. Misattribution of causation: Cultures of the pharynx, nasopharynx, or nasal drainage are not reliable for determining the bacterial etiology of AOM 1

2. Overlooking resistance patterns: The increasing prevalence of antibiotic-resistant strains must be considered when selecting therapy, particularly in recurrent cases

3. Failure to recognize shifting patterns: The microbiology of AOM continues to evolve with vaccination practices, requiring ongoing surveillance and potential adjustments to empiric therapy