A 5-year-old child presents with acute onset otalgia, fever (38.5°C), and conductive hearing loss. Otoscopy reveals a bulging, hyperemic tympanic membrane with loss of landmarks. Which of the following is NOT a typical feature of acute suppurative otitis media?

## Acute Suppurative Otitis Media — Typical Features ### Correct Answer: S. aureus as Most Common Organism **Key Point:** The most common causative organisms in acute suppurative otitis media are *Streptococcus pneumoniae* and *Haemophilus influenzae* (non-typeable), NOT *Staphylococcus aureus*. S. aureus is a secondary pathogen and is seen in chronic suppurative otitis media or when there is tympanic perforation with external ear involvement. ### Why the Other Options Are Correct Features | Feature | Explanation | |---------|-------------| | **Air-fluid level on X-ray** | Fluid accumulation in the middle ear creates a characteristic air-fluid level on lateral skull X-ray (Schuller's view). This is a classic radiological sign of ASOM. | | **Positive Rinne test (BC > AC)** | Conductive hearing loss occurs due to fluid in the middle ear and stiffening of the ossicular chain. Bone conduction remains intact, so BC > AC (abnormal Rinne). | | **Pus under pressure** | The tympanic membrane bulges because pus accumulates under pressure in the middle ear space. The pars tensa is more compliant and bulges before perforation occurs. | ### Microbiology of ASOM **High-Yield:** The classic triad of pathogens in acute suppurative otitis media: 1. *Streptococcus pneumoniae* — ~30–40% (most common) 2. *Haemophilus influenzae* (non-typeable) — ~30–40% 3. *Moraxella catarrhalis* — ~10–15% **Clinical Pearl:** *Staphylococcus aureus* becomes relevant in: - Chronic suppurative otitis media - Post-perforation discharge - Malignant otitis externa (in diabetics) - Secondary infection after trauma ### Pathophysiology of Bulging Tympanum 1. Tubal obstruction (viral URI, adenoiditis) → negative middle ear pressure 2. Bacterial invasion → suppuration and pus formation 3. Pus accumulates under increasing pressure 4. Tympanic membrane stretches and bulges (pars tensa is the weakest point) 5. If untreated → spontaneous perforation (usually in posterosuperior quadrant) **Mnemonic: ASOM Pathogens = "SPM"** - **S**treptococcus pneumoniae - **P**seudomonas (rare in acute; common in chronic) - **M**oraxella catarrhalis - (Plus *H*aemophilus influenzae — the "H" is silent in this mnemonic!)