Impetigo

Overview

Non-bullous vs bullous impetigo
FeatureNon-bullousBullous
Causative organismS. aureus + S. pyogenesS. aureus (phage group II, toxin-producing)
Hallmark lesionHoney-coloured (golden) crustingFlaccid bullae with collarette on erythematous base
DistributionPerioral and perinasal - classic in childrenAny site
FeverUncommonMay occur
ScarringNone (unless ecthyma develops)None (unless ecthyma develops)
•Pruritus - both types; scratching causes satellite lesions (autoinoculation)
•Clinical diagnosis - no investigations needed in uncomplicated first presentation

Investigations

•Skin swab (MC&S) - only if persistent, recurrent, widespread, or treatment failure; identifies MRSA or resistant organisms

Management

•Hygiene and exclusion - handwashing, no shared towels, keep nails short; exclude from school/nursery until lesions crusted and dry OR 48 hours after starting treatment
First-line · localised non-bullous, non-immunocompromised
  1. 1Hydrogen peroxide 1% cream - apply 2-3 times daily for 5 days
Second-line · if hydrogen peroxide unsuitable or failed
  1. 1Fusidic acid 2% cream - 3 times daily for 5 days
  2. 2Mupirocin 2% cream - reserved for fusidic acid resistance or MRSA
Third-line · oral antibiotics
  1. 1Indicated for: bullous impetigo, widespread non-bullous, failed topical treatment, immunocompromised
  2. 2Flucloxacillin - first choice (covers S. aureus)
  3. 3Cefalexin - penicillin allergy without anaphylaxis risk
  4. 4Clarithromycin or erythromycin - penicillin allergy with anaphylaxis risk
•Treat underlying skin disease - optimise eczema management (emollients, topical steroids) to prevent recurrent secondary impetigo
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Reassess if no improvement after completing treatment - take a swab at this point. Refer to secondary care for suspected systemic complications (sepsis, glomerulonephritis, deeper soft tissue infection) or immunocompromised patients with widespread infection.

Complications

•Post-streptococcal glomerulonephritis - immune complex-mediated; 1-3 weeks after S. pyogenes infection; haematuria, proteinuria, hypertension, oedema
•Ecthyma - deeper ulcerating form into dermis; punched-out ulcers with grey-yellow crust; heals with scarring
•Cellulitis - spread into deeper dermis; spreading erythema, warmth, tenderness, systemic features
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Antibiotic treatment of streptococcal impetigo does NOT reliably prevent post-streptococcal glomerulonephritis (unlike streptococcal pharyngitis where treatment reduces rheumatic fever risk). Always check urine in children with recent impetigo who develop oedema or hypertension.