Impetigo is a highly contagious, superficial bacterial skin infection primarily affecting young children aged 2 to 5 years, though older children and adults remain susceptible. Understanding its variants, diagnosis, targeted therapy, and containment strategies is critical to managing outbreaks and avoiding unnecessary systemic antibiotic use.
Etiology & Pathophysiology
Impetigo is caused by Staphylococcus aureus and/or Group A Beta-Hemolytic Streptococcus (GAS; Streptococcus pyogenes). Infection typically occurs following minor epidermal barrier breakdown (e.g., abrasions, insect bites, scratches, eczema), but can also colonize intact skin.
1. Clinical Presentation: Nonbullous vs. Bullous Impetigo
| Feature | Nonbullous Impetigo (70% of Cases) | Bullous Impetigo |
|---|---|---|
| Primary Pathogen | S. aureus, Group A Streptococcus, or co-infection | Exfoliative toxin-producing S. aureus strains |
| Pathomechanics | Direct bacterial invasion of superficial epidermis | Exfoliative toxins target desmoglein-1, splitting the upper epidermal layer |
| Classic Appearance | Small papules/vesicles rupture into superficial lesions with honey-colored (golden) crusts ⭐ | Large, fragile, fluid-filled bullae (clear to cloudy) that rupture, leaving shallow raw erosions |
| Typical Locations | Perioral and perinasal facial regions, exposed limbs | Trunk, intertriginous areas, extremities |
🚨 Red Flag Escalation: Deep Tissue Invasion & Systemic Signs
Uncomplicated impetigo is strictly localized and rarely presents with fever or constitutional symptoms. Clinicians must evaluate for potential complications or alternative diagnoses if red flags emerge:
- Ecthyma: A deeper ulcerative form of impetigo extending into the dermis, leaving punched-out ulcers with thick crusts and scarring.
- Cellulitis / Erysipelas: Rapidly spreading erythema, warmth, severe pain, induration, or high fever.
- Post-Streptococcal Glomerulonephritis (PSGN): A rare late non-suppurative complication following Group A Strep impetigo (monitor for hematuria/edema).
2. Diagnostic Approach & MRSA Considerations
Diagnosis is predominantly clinical based on characteristic lesion morphology and location.
| Diagnostic Strategy | Indications & Clinical Context |
|---|---|
| Clinical Diagnosis | Sufficient for uncomplicated cases presenting with classic honey-colored crusts or intact bullae. Routine culture is unnecessary. |
| Bacterial Culture & Sensitivity | Indicated when:
• First-line empic treatment fails • Infection repeatedly recurs • Local outbreak monitoring is required • Suspected Methicillin-Resistant S. aureus (MRSA) |
3. Evidence-Based Treatment Protocol
| Severity / Extent | Recommended Regimen | Clinical Notes |
|---|---|---|
| Localized / Limited Lesions (Nonbullous) |
Topical Antibiotic Ointment • Mupirocin 2% ointment • Retapamulin 1% ointment |
First-line standard of care. Applied directly to cleaned, debrided crusts to avoid systemic side effects. |
| Extensive / Bullous / Outbreak | Oral Antibiotics • Cephalexin • Dicloxacillin • Clindamycin or Trimethoprim-Sulfamethoxazole (if MRSA suspected) |
Indicated for widespread lesions, bullous form, multiple household members affected, or failed topical therapy. |
Mnemonic: CRUST – Infection Control & Home Care
- C – Clean & Cover: Gently cleanse affected areas with mild soap and water; cover loosely with clean bandages.
- R – Restrict Sharing: Do not share towels, washcloths, clothing, or bedding with household members.
- U – Uncut Nails Hazard: Keep fingernails short and clean to prevent autoinoculation and secondary trauma from scratching.
- S – Sanitization: Frequent hand hygiene with soap/water or alcohol-based rubs, especially after touching lesions.
- T – Time to Return: Children may typically return to school or daycare after completing 24 hours of appropriate antibiotic therapy and when active lesions are covered.
High-Yield Exam & Practice Pearls
- Classic Landmark: Facial honey-colored (golden) crusted sores around the mouth/nose = Nonbullous Impetigo.
- Toxin Mechanism: Bullous impetigo is mediated by S. aureus exfoliative toxins cleavage of desmoglein-1 in the superficial epidermis.
- First-Line Topical: Mupirocin ointment is preferred for limited nonbullous lesions over oral regimens to reduce antibiotic resistance.
- Deep Form Warning: Ulcerative lesions extending through the epidermis into the dermis represent Ecthyma, which heals with scarring.
- Transmission Control: Infection remains highly contagious until 24 hours after initiating effective antibiotic treatment.
