Impetigo

Aetiology of Impetigo

• General Information
  • Primarily affects children, highly contagious.
• Types of Impetigo
  • Crusted or Nonbullous Impetigo
    • Presents with yellow crusts, erosions, itchy or irritating but not painful.
  • Bullous Impetigo
    • Features rapid-eroding irritating blisters, usually caused by Staphylococcus aureus.
• Causative Agents
  • Nonendemic Settings:
    • Primarily S. aureus.
    • Less commonly Streptococcus pyogenes (Group A Streptococcus).
    • Possible co-infection with both bacteria.
  • Endemic Settings:
    • Typically S. pyogenes, even if S. aureus is identified, including CA-MRSA.
• Complications
  • Wider spread infection: cellulitis, lymphangitis, and bacteraemia.
  • Staphylococcal scalded skin syndrome.
  • Scarlet fever.
  • Post-streptococcal glomerulonephritis: a rare, acute renal condition following infection with Streptococcus pyogenes (group A streptococcus). This is due to a type III hypersensitivity reaction and presents 2–6 weeks post-skin infection.
  • Streptococcal toxic shock syndrome: a rare complication causing diffuse erythematous rash, hypotension, and pyrexia.
  • Postinflammatory pigmentation.
  • Scarring, particularly with ecthyma.

Approach to Managing Impetigo

• Treatment Requirement: Antibiotic treatment is necessary for all impetigo cases.
• Initial Management:
  • Mild impetigo: Start empirical antibiotic therapy without initial skin swab; swab if no response.
  • Severe disease: Require skin swab for culture and testing before empirical therapy.
• Associated Conditions: Treat underlying dermatosis if present (e.g., dermatitis, scabies, head lice).
• General measures
  • Regular gentle cleansing; removal of honey-coloured crusts.
  • Practice good hand hygiene and keep fingernails cut short.
  • Cover the affected areas with watertight dressing to prevent spread. 

Preventative measures

• Avoid touching affected areas.
• Practice good hand hygiene; wash hands before and after applying creams.
• Use a clean cloth each time to wash and dry affected areas.
• Do not share towels or face cloths.
• Clothing and bedding should be changed daily; wash using hot temperatures.
• Avoid close contact with others — school/nursery children should stay home until lesions have crusted over, or they have received at least 24 hours of treatment. 

Outcome

• Impetigo is usually self-limiting without serious complications. Without treatment, impetigo usually heals in 2–3 weeks; with treatment lesions resolve within 10 days.
• Postinflammatory hypopigmentation or hyperpigmentation may occur but scarring is uncommon.
• Recurrent impetigo may indicate nasal carriage of S. aureus. Following treatment, eradication of staphylococcal carriage may be necessary.

Antibiotic Therapy for Impetigo (Including Dosages – from eTG)

• Nonendemic Settings:
  • Localised Sores:
    • Mupirocin 2% ointment or cream, apply topically 8-hourly for 5 days.
  • Multiple Sores or Recurrent Infection:
    • Dicloxacillin 500 mg (child: 12.5 mg/kg up to 500 mg) orally, 6-hourly for 7 days.
    • Flucloxacillin 500 mg (child: 12.5 mg/kg up to 500 mg) orally, 6-hourly for 7 days.
    • Cefalexin 500 mg (child: 12.5 mg/kg up to 500 mg) orally, 6-hourly for 7 days, or 1 g (child: 25 mg/kg up to 1 g) orally, 12-hourly for 7 days.
    • For penicillin-allergic patients: Trimethoprim+sulfamethoxazole (TMP-SMX) 160+800 mg (child 1 month or older: 4+20 mg/kg up to 160+800 mg) orally, 12-hourly for 3 days, or 320+1600 mg (child 1 month or older: 8+40 mg/kg up to 320+1600 mg) orally, daily for 5 days.
• Endemic Settings:
  • Benzathine benzylpenicillin (single dose intramuscularly): Adult: 1.2 million units; Child <10 kg: 0.45 million units; Child 10 kg to <20 kg: 0.6 million units; Child ≥20 kg: 1.2 million units.
  • TMP-SMX 160+800 mg (child 1 month or older: 4+20 mg/kg up to 160+800 mg) orally, 12-hourly for 3 days, or 320+1600 mg (child 1 month or older: 8+40 mg/kg up to 320+1600 mg) orally, daily for 5 days.