A 4-year-old boy from rural Maharashtra presents with honey-colored crusted lesions on his face and forearms following a minor cut sustained during play. Culture confirms *Staphylococcus aureus*. Regarding the management and complications of impetigo, all of the following are true EXCEPT:

Explanation

## Management and Complications of Impetigo ### Treatment Algorithm ```mermaid flowchart TD A[Impetigo diagnosed]:::outcome --> B{Extent of disease?}:::decision B -->|Localized: <2% BSA| C[Topical mupirocin TID × 7 days]:::action B -->|Moderate: 2-10% BSA| D[Topical + oral antibiotic]:::action B -->|Extensive: >10% BSA| E[Systemic antibiotic only]:::action C --> F{Response at 7 days?}:::decision F -->|Yes| G[Continue topical]:::action F -->|No| H[Switch to systemic]:::action D --> I[Oral cephalexin or amoxicillin-clavulanate]:::action E --> J[Cephalexin, amoxicillin-clavulanate, or clindamycin]:::action I --> K[Review at 7 days]:::outcome J --> K ``` ### First-Line Topical Therapy **Key Point:** Topical mupirocin (Bactroban) is the gold standard for localized impetigo: - **Indication:** <2% body surface area involvement - **Dosing:** Apply TID (three times daily) for 7–10 days - **Efficacy:** 95% cure rate for non-bullous impetigo - **Advantage:** Minimal systemic absorption; low resistance rates ### Systemic Antibiotic Therapy **High-Yield:** When topical therapy is inadequate or lesions are extensive (>2% BSA): | Antibiotic | Dosing | Notes | | --- | --- | --- | | **Cephalexin** (1st-line) | 25–50 mg/kg/day ÷ 4 doses | Excellent for *S. aureus* and *S. pyogenes* | | **Amoxicillin-clavulanate** (1st-line) | 25–45 mg/kg/day ÷ 3 doses | Covers β-lactamase-producing *S. aureus* | | **Clindamycin** | 10–13 mg/kg/day ÷ 3 doses | Reserve for MRSA or penicillin allergy | | **Azithromycin** | 5–12 mg/kg/day × 5 days | Alternative if allergy; increasing resistance | **Warning:** Penicillin V and amoxicillin (without clavulanate) are NOT recommended due to widespread β-lactamase-producing *S. aureus*. ### Complications of Impetigo #### Post-Streptococcal Glomerulonephritis (PSGN) **Clinical Pearl:** PSGN is a well-recognized complication of impetigo caused by **nephritogenic strains of *Streptococcus pyogenes*** (e.g., M types 2, 49, 57, 60). However, PSGN risk is **much lower with impetigo** (~5–10%) compared to streptococcal pharyngitis (~10–15%), because *S. pyogenes* is now a secondary pathogen in most impetigo cases. **Key Point:** PSGN does NOT occur with *Staphylococcus aureus* impetigo. Since this patient's culture is positive for *S. aureus*, PSGN risk is negligible. #### Local and Invasive Complications **High-Yield:** While impetigo can progress to cellulitis, abscess formation, or bacteremia, **parenteral antibiotics are NOT required in all cases**. The decision to use parenteral therapy depends on: - Severity of systemic symptoms (fever, malaise) - Presence of signs of invasive infection (cellulitis, lymphadenitis, bacteremia) - Immunocompromise - Failure of oral therapy **Mnemonic: SCAB** — Signs of systemic infection, Cellulitis, Abscess, Bacteremia (indicators for parenteral therapy) Most uncomplicated impetigo cases respond well to topical or oral antibiotics without parenteral therapy. ### Why Option 4 Is Wrong **Warning:** Option 4 states that impetigo caused by *S. aureus* "requires parenteral antibiotics in **all cases**." This is **incorrect and overly broad**. While *S. aureus* impetigo can progress to invasive disease, the vast majority of cases respond to topical or oral antibiotics. Parenteral therapy is reserved for: - Systemic toxicity (fever, sepsis) - Evidence of invasive infection (cellulitis, abscess, bacteremia) - Immunocompromised patients - Failure of oral therapy after 7 days The blanket statement "in all cases" is inaccurate and would lead to unnecessary hospitalization and antibiotic escalation. ### Correct Features (Options 1, 2, 3) - **Option 1:** Accurate — topical mupirocin is first-line for localized impetigo (<2% BSA) - **Option 2:** Accurate — PSGN is a recognized complication of *S. pyogenes* impetigo with 5–10% incidence - **Option 3:** Accurate — oral cephalexin is a first-line systemic antibiotic when topical therapy is inadequate [cite:Fitzpatrick's Dermatology 9e Ch 189; Harrison 21e Ch 119]