A 6-year-old child presents with honey-crusted lesions on the face and exposed areas of the body for 3 days. The lesions are non-bullous and painless. Which investigation is most appropriate to confirm the diagnosis and guide antibiotic therapy?

Question

Accepted Answer

D. Gram stain and culture from the lesion. ## Investigation of Choice in Non-Bullous Impetigo

**Key Point:** Gram stain and culture from the lesion is the gold standard for confirming bacterial impetigo and identifying the causative organism (Staphylococcus aureus or Streptococcus pyogenes).

### Why Gram Stain and Culture?

1. **Organism Identification**
   - Gram stain shows Gram-positive cocci in clusters (S. aureus) or chains (S. pyogenes)
   - Culture confirms the organism and allows antibiotic susceptibility testing (AST)
   - Essential in the era of MRSA to guide empiric therapy

2. **Antibiotic Susceptibility Testing**
   - Determines resistance patterns (β-lactamase, MRSA, etc.)
   - Guides choice between β-lactams, cloxacillin, or glycopeptides
   - Reduces treatment failure and prevents resistance spread

3. **Clinical Correlation**
   - Non-bullous impetigo (70% of cases) typically caused by S. aureus
   - Bullous impetigo caused by exfoliative toxin-producing S. aureus
   - Culture differentiates from other bacterial skin infections

**High-Yield:** In India, MRSA prevalence in community impetigo is rising; culture-guided therapy is increasingly important.

### Specimen Collection
- Swab the base of the lesion (not the crust alone)
- Transport in sterile tube or culture medium
- Best yield before topical antibiotics are applied

**Clinical Pearl:** In uncomplicated non-bullous impetigo with typical presentation, empiric topical antibiotics (mupirocin) may be started; culture confirms diagnosis and guides escalation if needed.

[cite:Fitzpatrick's Dermatology in General Medicine Ch 195]

![Impetigo and Staphylococcal Skin Infections diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/3341.webp)

Answer

A. KOH mount preparation

Answer

B. Tzanck smear

Answer

C. Bacterial antigen detection by ELISA

A 6-year-old child presents with honey-crusted lesions on the face and exposed areas of the body for 3 days. The lesions are non-bullous and painless. Which investigation is most appropriate to confirm the diagnosis and guide antibiotic therapy?

Explanation

Investigation of Choice in Non-Bullous Impetigo

Why Gram Stain and Culture?

Specimen Collection

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