## Causative Organisms of Impetigo **Key Point:** Staphylococcus aureus is now the most common cause of impetigo globally, accounting for 70–80% of cases, surpassing Streptococcus pyogenes in prevalence over the past two decades. ### Historical vs. Current Epidemiology | Organism | Historical Role | Current Status | Prevalence | |----------|-----------------|----------------|------------| | **S. aureus** | Secondary invader | Primary pathogen | 70–80% | | **S. pyogenes** | Classic cause | Declining | 10–20% | | **MRSA** | Emerging | Increasingly common | Variable by region | ### Clinical Features of S. aureus Impetigo 1. **Presentation:** Honey-crusted or golden-yellow crusts on intact skin or erosions 2. **Sites:** Face, exposed areas, areas of minor trauma 3. **Age:** Most common in children aged 2–6 years 4. **Contagiousness:** Highly contagious; spreads via direct contact **High-Yield:** The shift from S. pyogenes to S. aureus as the leading cause reflects the rise of community-acquired methicillin-resistant S. aureus (CA-MRSA) strains, which now dominate in many regions including India. **Clinical Pearl:** S. aureus impetigo often presents with bullous lesions (bullous impetigo) due to exfoliative toxins (exfoliative toxin A and B), whereas S. pyogenes typically causes non-bullous impetigo with thinner, more friable crusts. **Warning:** Do not assume S. pyogenes is the most common cause based on older textbooks; epidemiology has shifted significantly since the 1990s–2000s.
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