## Microbiology of Acute Suppurative Otitis Media **Key Point:** Streptococcus pneumoniae remains the most common bacterial pathogen in acute suppurative otitis media (ASOM) globally, despite pneumococcal vaccination programs. ### Epidemiology and Frequency | Organism | Frequency (%) | Age Group | Clinical Context | |----------|---------------|-----------|------------------| | *Streptococcus pneumoniae* | 40–50 | All ages, peak 6 mo–3 yr | Most common; invasive potential | | *Haemophilus influenzae* (non-typeable) | 25–35 | Children <5 yr | Second most common | | *Moraxella catarrhalis* | 10–15 | Infants and young children | Gram-negative diplococcus | | *Streptococcus pyogenes* | 5–10 | School-age children | Post-viral URTI | | *Pseudomonas aeruginosa* | <5 | Chronic/recurrent OM | Malignant otitis externa, not typical ASOM | **High-Yield:** The "Big 3" organisms in ASOM are *S. pneumoniae*, non-typeable *H. influenzae*, and *M. catarrhalis*. *S. pneumoniae* consistently ranks first in incidence and severity. ### Clinical Significance **Clinical Pearl:** *S. pneumoniae* is associated with: - More severe symptoms and higher fever - Greater risk of spontaneous perforation - Potential for intracranial complications (meningitis, subdural empyema) - Higher antibiotic resistance rates (penicillin-resistant strains) **Mnemonic:** **PHM** = *Pneumococcus*, *Haemophilus* (non-typeable), *Moraxella* — the three most common causes of ASOM in children. ### Why *S. pneumoniae* Dominates 1. **Pathogenic virulence:** Polysaccharide capsule and pneumolysin toxin facilitate invasion 2. **Eustachian tube dysfunction:** Follows viral URTIs; *S. pneumoniae* colonizes nasopharynx 3. **Age-related susceptibility:** Peak incidence 6 months–3 years (immature immune response) 4. **Vaccine impact:** Even with PCV13/PPSV23, non-vaccine serotypes persist [cite:Scott-Brown's Otolaryngology 8e Ch 2.3] ---
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.