A 4-year-old child presents with honey-crusted lesions on the face and exposed areas. Which is the most common causative organism of this presentation?

Explanation

## Most Common Cause of Impetigo **Key Point:** Staphylococcus aureus is now the most common causative organism of impetigo globally, accounting for >70% of cases, including both non-bullous (70%) and bullous (95%) forms. ### Historical Context Historically, Streptococcus pyogenes (Group A Streptococcus) was the predominant pathogen, but the epidemiology has shifted dramatically over the past two decades due to: - Increased prevalence of methicillin-resistant S. aureus (MRSA) strains - Better antibiotic coverage against streptococci - Increased carriage rates of S. aureus in the community ### Clinical Presentation | Feature | Non-bullous Impetigo | Bullous Impetigo | |---------|----------------------|------------------| | Frequency | 70% of cases | 30% of cases | | Causative organism | S. aureus (most common) | S. aureus (95%) | | Toxin involved | — | Exfoliative toxin (ETA/ETB) | | Appearance | Honey-crusted lesions | Flaccid blisters, erosions | **High-Yield:** The honey-coloured crust described in the stem is pathognomonic for impetigo and is most commonly caused by S. aureus in the modern era. **Clinical Pearl:** While S. pyogenes can still cause impetigo (especially in tropical regions with poor hygiene), S. aureus is now the global standard answer for "most common cause of impetigo." ### Why S. aureus Dominates 1. Produces multiple virulence factors (α-toxin, Panton-Valentine leukocidin in some strains) 2. Better ability to invade intact skin compared to S. pyogenes 3. Increased prevalence in skin carriage (up to 30% of population) 4. MRSA strains are now community-acquired, not just hospital-associated