A 6-year-old girl presents with a 5-day history of left ear pain, purulent discharge from the ear canal, and fever (38.5°C). Her parents report she had a cold 2 weeks prior. On otoscopy, the tympanum shows a small perforation with pus draining from the middle ear. Audiometry shows a 25 dB conductive hearing loss. What is the most likely organism and the recommended first-line antibiotic?

Explanation

## Microbiology of Acute Suppurative Otitis Media **Key Point:** In children with ASOM, the three most common causative organisms are *Streptococcus pneumoniae* (30–50%), *Haemophilus influenzae* non-typeable (20–30%), and *Moraxella catarrhalis* (10–15%). ## Organism Identification in ASOM | Organism | Clinical Context | Antibiotic of Choice | |----------|------------------|----------------------| | *S. pneumoniae* (most common) | ASOM in children, recent URI | Amoxicillin or amoxicillin-clavulanate | | *H. influenzae* (non-typeable) | ASOM, URI prodrome | Amoxicillin-clavulanate or cephalosporin | | *M. catarrhalis* | ASOM, often β-lactamase producer | Amoxicillin-clavulanate | | *P. aeruginosa* | Chronic suppurative otitis media, water exposure | Fluoroquinolone (ciprofloxacin) or aminoglycoside | | *S. aureus* | Post-traumatic, post-surgical, immunocompromised | Cloxacillin or vancomycin | **High-Yield:** ASOM = *S. pneumoniae* or *H. influenzae*. Chronic suppurative otitis media = *P. aeruginosa*. This patient has **acute** disease with perforation — classic for *S. pneumoniae*. ## Why Amoxicillin-Clavulanate? 1. **Covers *S. pneumoniae*** — the most likely pathogen 2. **Covers *H. influenzae* and *M. catarrhalis*** — both produce β-lactamase; clavulanate inhibits this 3. **Oral bioavailability** — suitable for outpatient management of ASOM with perforation 4. **First-line guideline recommendation** — per AAO-HNS and Indian ENT guidelines **Clinical Pearl:** Once the tympanum perforates, pain typically resolves (pressure relief) and drainage begins. The goal shifts to eradicating the infection and allowing the perforation to heal. Oral antibiotics are adequate if the child is systemically well. **Mnemonic:** **AOM-HIP** = *S. pneumoniae*, *H. influenzae*, *M. catarrhalis* — the "HIP" trio causing acute otitis media in children. Amoxicillin-clavulanate covers all three.