Regarding the clinical features and epidemiology of impetigo, all of the following statements are correct EXCEPT:

Explanation

## Epidemiology and Microbiology of Impetigo ### Causative Organisms **Key Point:** The epidemiology of impetigo has shifted significantly over the past two decades. Historically, *Streptococcus pyogenes* (Group A Streptococcus) was the dominant pathogen, but *Staphylococcus aureus* is now the leading cause globally, particularly in developed nations. | Feature | Non-bullous Impetigo | Bullous Impetigo | | --- | --- | --- | | **Frequency** | ~70% of cases | ~30% of cases | | **Primary Organism** | *S. aureus* (most common); *S. pyogenes* (less common) | *S. aureus* exclusively | | **Pathogenic Mechanism** | Direct invasion of epidermis | Exfoliative toxins (ETA, ETB) cause intra-epidermal acantholysis | | **Blister Character** | Pustules, crusts, honey-colored | Flaccid, clear blisters | | **Depth of Lesion** | Subcorneal to mid-epidermal | Subcorneal (superficial) | ### Clinical Presentation **High-Yield:** Impetigo predominantly affects children aged 2–6 years. Lesions favor warm, moist areas and sites of minor trauma: - Face (especially around nose and mouth) - Lower extremities and shins - Areas with breaks in skin barrier ### Why Option 4 Is Wrong **Clinical Pearl:** While *S. pyogenes* was historically the dominant organism (pre-1990s), *Staphylococcus aureus* now accounts for the majority of impetigo cases in most developed countries and increasingly in developing nations. The statement claiming *S. pyogenes* causes >80% of cases is **outdated and factually incorrect** by current epidemiological data. In many regions, *S. aureus* (including MRSA strains) causes 60–90% of impetigo cases. **Warning:** Exam writers often test knowledge of this epidemiological shift. Candidates who rely on older textbooks may incorrectly select *S. pyogenes* as the primary pathogen. ### Correct Features (Options 1, 2, 3) - **Option 1:** Accurate — non-bullous impetigo is most common (~70%) and *S. aureus*-driven - **Option 2:** Accurate — bullous impetigo results from exfoliative toxins causing flaccid blisters - **Option 3:** Accurate — peak age 2–6 years; predilection for face and lower extremities [cite:Fitzpatrick's Dermatology 9e Ch 189]