Impetigo

Impetigo is an infectious, predominantly pediatric skin disease caused by the bacteria Staphylococcus aureus or, less commonly, Streptococcus pyogenes. There are both bullous and nonbullous variants. The disease causes honey-colored, crusted lesions with surrounding erythema and typically affects the face, but may also manifest on the extremities. While the diagnosis is usually made based on clinical findings, it can be confirmed with a bacterial culture. The first-line treatment for mild impetigo is a topical antibiotic (mupirocin), which typically resolves the infection without complications. An additional systemic antibiotic may be indicated in more severe cases.

• Age
  • Primarily affects children (especially between 2–6 years of age) ^[1]
  • Impetigo is highly contagious and can cause epidemics in preschools or schools. ^[2]
• Prevalence: high in resource-limited countries

Impetigo is the most common bacterial skin infection among children.

Epidemiological data refers to the US, unless otherwise specified.

• Pathogens: superficial bacterial skin infection
  • Staphylococcus aureus: ∼ 80% of cases
    • Causes both bullous impetigo and nonbullous impetigo
    • S. aureus strains that produce exfoliative toxins A and B are responsible for bullous impetigo. ^[3][4]
  • Streptococcus pyogenes (GAS); : ∼ 10% of cases: causes nonbullous impetigo only
  • S. aureus and GAS coinfection: ∼ 10% of cases
• Predisposing factors
  • Warm and humid climate
  • Crowded, unsanitary living conditions
  • Poor personal hygiene
  • Medical conditions
    • Pre-existing skin lesions (e.g., atopic dermatitis, scabies, insect bites, abrasions, eczema)
    • Diabetes mellitus
    • Immunodeficiency (e.g., HIV, post-organ transplantation, systemic corticosteroids)
• Route of infection
  • Primary impetigo: bacterial infection of previously healthy skin
  • Secondary impetigo (impetiginization): secondary infection of pre-existing skin lesions

• Rare manifestation: ecthyma
  • Ulcerative impetigo that extends into the dermis
  • Manifests as a coin-sized, superficial ulcer with a punched-out appearance

Impetigo should be suspected in children presenting with honey-colored crusts around the mouth and nose.

• Generally diagnosed based on clinical presentation
• Microbiological culture ^[10]
  • Assists with detection of the causative pathogen
  • Indications: inconclusive diagnosis, recurrence despite treatment

See “Differential diagnosis of scaling.” ^[5][11]

See “Blistering skin diseases”.

• Conditions that cause localized inflammation
  • Atopic dermatitis
  • Contact dermatitis
  • Seborrheic dermatitis
  • Cutaneous candidiasis
  • Tinea
  • Herpes simplex virus infection
  • Erysipelas
  • Folliculitis
• Conditions that cause bullae
  • Pemphigus vulgaris and bullous pemphigoid
  • Bullous drug reactions
  • Insect bites or burns
  • Varicella

The differential diagnoses listed here are not exhaustive.

• General: wound cleansing with antibacterial washes (e.g., chlorhexidine)
• Mild nonbullous impetigo: (single lesions or small areas affected): topical antibiotics (mupirocin, retapamulin)
• Bullous impetigo, ecthyma, or severe nonbullous impetigo (widespread dispersion, numerous lesions, and/or fever)
  • First-line treatment : first generation cephalosporins (e.g., cephalexin; ) or dicloxacillin ^[10]
  • Alternative: amoxicillin-clavulanate, macrolides ^[12]
  • If MRSA infection; is confirmed or suspected : clindamycin, trimethoprim-sulfamethoxazole, doxycycline ^[10]

• In GAS infections: acute poststreptococcal glomerulonephritis (PSGN)
• Very rarely: staphylococcal scalded skin syndrome (SSSS)
• Superinfection ^[10]

We list the most important complications. The selection is not exhaustive.

• Advise patients and caregivers to wash hands regularly.
• To prevent the spread of the disease, children should receive antibiotic treatment for at least 24 hours before returning to daycare or school.