Impetigo (School Sores)

Overview – Impetigo

Impetigo is a highly contagious superficial bacterial skin infection, predominantly affecting young children. It is frequently seen in school-aged populations and is easily transmitted through direct skin contact or shared items. While usually self-limiting, appropriate treatment is important to prevent spread and complications such as post-streptococcal glomerulonephritis. This topic is highly relevant for final-year medical students in paediatrics, dermatology, and general practice rotations.

Definition

Impetigo is a superficial, contagious bacterial skin infection that presents as vesicles, pustules, and honey-coloured crusts.

Aetiology

• Bacterial origin:
  • Staphylococcus aureus (most common)
  • Streptococcus pyogenes (especially in non-bullous and ulcerative forms)
• Predisposing factors:
  • Poor hygiene
  • Crowded living conditions
  • Skin trauma (e.g., insect bites, eczema)

Epidemiology

• Most common in preschool and primary school-aged children
• Endemic in warm, humid climates
• Outbreaks often occur in settings with close contact (e.g. schools, daycares)
• High burden in Aboriginal and Torres Strait Islander communities

Pathophysiology

• Colonisation or invasion of epidermis by S. aureus or S. pyogenes
• Disruption of the skin barrier (e.g., scratching, eczema) facilitates entry
• Inflammatory response results in vesicles/pustules → rupture → crust formation
• S. pyogenes infections may trigger immune complications (e.g. acute glomerulonephritis)

Clinical Features

1. Non-Bullous (Crusted) Impetigo

• Most common form
• Begins as small red papules or vesicles → rapidly rupture
• Honey-yellow crusts on an erythematous base
• Often on the face, around nose and mouth
• Pruritic, but not painful
• Caused by S. aureus or S. pyogenes

2. Bullous Impetigo

• Always caused by S. aureus (produces exfoliative toxin)
• Flaccid, fluid-filled bullae (larger than vesicles)
• Rupture leaves shallow erosions with thin brown crust
• Less common, but more common in neonates

3. Ulcerative (Ecthyma)

• Always caused by S. pyogenes
• Deeper infection with punched-out ulcers covered by crust
• More common in tropical climates and remote communities

Diagnosis

• Clinical diagnosis is usually sufficient
• Swabs for bacterial culture if:
  • Recurrent or resistant cases
  • Concern for MRSA
  • Widespread infection
• Consider testing for post-streptococcal complications (e.g., urine dipstick) if systemic signs present

Management

General Measures

• Cover affected areas with dressings
• Advise temporary exclusion from school or daycare until lesions are crusted/dry
• Emphasise good hygiene: handwashing, no towel sharing

Medical Treatment

• Topical antibiotics (mild/localised):
  • Mupirocin or fusidic acid cream
• Oral antibiotics (widespread/systemic symptoms):
  • Cephalexin or flucloxacillin
  • Consider trimethoprim-sulfamethoxazole if MRSA suspected
• Treat underlying skin conditions (e.g., eczema)

Complications

• Post-streptococcal glomerulonephritis (non-bullous form)
• Rheumatic fever (rare, in high-risk groups)
• Cellulitis or deeper soft tissue infection
• MRSA colonisation

Prevention

• Improved hygiene and handwashing
• Avoid scratching lesions
• Early treatment to prevent transmission
• In high-risk communities, public health interventions may be needed

Summary – Impetigo

Impetigo is a highly contagious superficial bacterial infection most common in school-aged children. It typically presents with vesicles and crusts on the face and limbs and is caused by Staphylococcus aureus or Streptococcus pyogenes. It is usually self-limiting, but topical or systemic antibiotics are used to hasten recovery and limit transmission. See our Skin & Dermatology Overview page for more related topics.