A 6-year-old girl from Delhi presents with a 5-day history of right ear discharge, fever, and hearing loss. Her parents report she had a cold 2 weeks ago. On examination, there is purulent discharge in the external auditory canal, and the tympanum appears perforated. Weber test lateralizes to the right ear, and Rinne test shows bone conduction better than air conduction on the right. Otoscopy confirms a central perforation. What is the most likely causative organism?

Explanation

## Clinical Diagnosis: Acute Suppurative Otitis Media with Perforation The presentation—recent URTI, fever, purulent ear discharge, central tympanic perforation, and conductive hearing loss—is consistent with acute suppurative otitis media (ASOM) that has progressed to spontaneous perforation. ## Causative Organisms in ASOM **Key Point:** The three most common bacterial pathogens in acute suppurative otitis media are *Streptococcus pneumoniae*, *Haemophilus influenzae* (nontypeable), and *Moraxella catarrhalis*. *Pseudomonas aeruginosa* is NOT a typical cause of acute otitis media; it is the hallmark organism of chronic suppurative otitis media or malignant otitis externa. ## Organism Frequency and Clinical Context | Organism | Frequency in ASOM | Clinical Context | Key Features | |----------|-------------------|------------------|---------------| | *Streptococcus pneumoniae* | 25–35% | Most common in children <5 years; post-URTI | Gram-positive diplococci; vaccine-preventable | | *Haemophilus influenzae* (nontypeable) | 20–30% | Common in all age groups; post-URTI | Gram-negative coccobacillus; β-lactamase variable | | *Moraxella catarrhalis* | 10–15% | Less virulent; often mixed infection | Gram-negative diplococcus; β-lactamase producer | | *Pseudomonas aeruginosa* | <5% in ASOM | Chronic suppurative otitis media, malignant otitis externa | Gram-negative rod; opportunistic | **High-Yield:** In a child with acute otitis media following URTI and spontaneous perforation, *Streptococcus pneumoniae* is the single most likely organism, especially in the Indian pediatric population where pneumococcal vaccination coverage varies. ## Mnemonic for ASOM Pathogens **"SHiM" (Streptococcus, Haemophilus, Moraxella)** - **S** = *Streptococcus pneumoniae* (most common) - **H** = *Haemophilus influenzae* (nontypeable) - **M** = *Moraxella catarrhalis* **Clinical Pearl:** *Pseudomonas aeruginosa* is a red flag for: - Chronic suppurative otitis media (CSOM) - Malignant otitis externa (in elderly or immunocompromised) - Recurrent/persistent infection despite antibiotics - Granulation tissue in the ear canal It is NOT typical of acute otitis media in an immunocompetent child. [cite:Harrison 21e Ch 394]