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?
A. Pseudomonas aeruginosa
B. Corynebacterium diphtheriae
C. Streptococcus pyogenes
D. Staphylococcus aureus
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
Table
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-YieldNEET PG
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
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