## Epidemiology of Acute Osteomyelitis in Children **Key Point:** Staphylococcus aureus is the most common causative organism of acute osteomyelitis in children globally, including India, accounting for 50–80% of cases. ### Organism-Specific Features | Organism | Frequency | Key Features | Typical Presentation | | --- | --- | --- | --- | | *Staphylococcus aureus* | 50–80% | β-lactamase producer; high affinity for bone; produces toxins (α, β, PVL) | Acute, rapidly progressive metaphyseal osteomyelitis | | *Streptococcus pyogenes* | 5–10% | Less common; usually follows skin infection | Subacute course | | *Escherichia coli* | 2–5% | Gram-negative; more common in neonates and immunocompromised | Rare in immunocompetent children | | *Mycobacterium tuberculosis* | <5% | Chronic, indolent; TB spine (Pott's disease) | Insidious onset over weeks–months | ### Pathophysiology 1. Hematogenous seeding to metaphyseal vessels (rich vascular supply, slow blood flow) 2. Bacterial proliferation and abscess formation 3. Increased intramedullary pressure → compromised blood supply → necrosis 4. Pus ruptures through cortex → subperiosteal abscess → periosteal lifting **High-Yield:** *S. aureus* produces bone-degrading enzymes and toxins that facilitate rapid invasion and destruction. MRSA prevalence is rising in India and affects antibiotic choice. **Clinical Pearl:** In children <5 years, *S. aureus* may seed the epiphysis (unlike older children), risking septic arthritis if metaphysis is intra-articular (hip, shoulder, ankle). [cite:Tuli's Orthopedics 5e Ch 5] 
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