## Microbiology of Acute Suppurative Otitis Media **Key Point:** Streptococcus pneumoniae remains the most common bacterial pathogen in acute suppurative otitis media (ASOM) in children, despite the introduction of pneumococcal conjugate vaccines (PCV7 and later PCV13). ### Common Bacterial Pathogens in ASOM | Pathogen | Frequency | Notes | |----------|-----------|-------| | *Streptococcus pneumoniae* | 25–35% | Most common; encapsulated gram-positive diplococcus | | *Haemophilus influenzae* (non-typeable) | 20–30% | Second most common; gram-negative coccobacillus | | *Moraxella catarrhalis* | 10–15% | Gram-negative diplococcus; more common in younger children | | *Group A Streptococcus* | <5% | Rare in ASOM; more common in acute mastoiditis | | Viruses (RSV, rhinovirus, influenza) | 50–70% | Often precedes bacterial infection | **High-Yield:** The "big three" bacterial pathogens in ASOM are *S. pneumoniae*, non-typeable *H. influenzae*, and *M. catarrhalis*. These account for >90% of culture-positive cases. **Clinical Pearl:** Although PCV vaccines have reduced invasive pneumococcal disease, *S. pneumoniae* remains the leading cause of ASOM because the vaccine does not prevent mucosal colonization or otitis media. ### Pathogenesis Context These pathogens typically ascend from the nasopharynx via the Eustachian tube, especially during upper respiratory infections when mucociliary clearance is impaired. 
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