A 4-year-old boy from rural Maharashtra presents with his mother to the outpatient clinic with multiple fluid-filled blisters on his left forearm and hand that appeared 3 days ago. The lesions are preceded by a small cut sustained while playing. On examination, there are honey-crusted erosions overlying erythematous patches. The child is afebrile. A Gram stain of the blister fluid shows Gram-positive cocci in clusters. What is the most likely causative organism and the recommended first-line treatment?

Explanation

## Diagnosis: Non-bullous Impetigo ### Clinical Presentation **Key Point:** The honey-crusted erosions on an erythematous base are pathognomonic for non-bullous impetigo, which accounts for ~70% of impetigo cases in India. The clinical triad: 1. Preceding minor trauma (cut while playing) 2. Rapid onset (3 days) 3. Honey-coloured crusts on erythematous base ### Microbiology **High-Yield:** Gram-positive cocci in clusters = *Staphylococcus aureus*. This is now the most common cause of impetigo globally, including in India, displacing *Streptococcus pyogenes*. | Feature | S. aureus | S. pyogenes | |---------|-----------|-------------| | Gram stain | Cocci in clusters | Cocci in chains | | Impetigo prevalence | ~70% (current) | ~30% | | Bullous impetigo | Common (exfoliative toxin) | Rare | | Non-bullous impetigo | Common | Less common | ### Treatment Algorithm ```mermaid flowchart TD A[Impetigo diagnosed]:::outcome --> B{Localized or extensive?}:::decision B -->|Localized lesions<br/>< 5 lesions| C[Topical antibiotic]:::action B -->|Extensive or systemic signs| D[Oral antibiotic]:::action C --> E[Mupirocin 2% TDS x 7 days]:::action D --> F[First-line: Oral cephalexin<br/>or amoxicillin-clavulanate]:::action F --> G[Dosing: 25-50 mg/kg/day<br/>divided TDS x 7 days]:::action G --> H[Covers S. aureus<br/>and S. pyogenes]:::outcome ``` **Key Point:** Oral cephalexin (a first-generation cephalosporin) is the preferred first-line oral agent for impetigo because it: - Covers both *S. aureus* and *S. pyogenes* - Has excellent skin penetration - Is well-tolerated in children - Is cost-effective in India **Clinical Pearl:** Although this child has localized lesions (one forearm), the presence of multiple lesions and the need for systemic coverage of both organisms makes oral cephalexin appropriate. Topical mupirocin alone may be considered for <5 lesions in a compliant family. ### Why Not Penicillin G? **Warning:** Intramuscular penicillin G is NOT first-line for impetigo because: - Many *S. aureus* strains are penicillin-resistant (β-lactamase producers) - Oral agents are preferred for non-severe impetigo - IM injection is unnecessary for localized skin infection Penicillin G remains useful for invasive streptococcal infections (cellulitis, erysipelas) but not for impetigo.