Impetigo

Impetigo is an infectious skin disease predominantly seen in children and caused by the bacteria Staphylococcus aureus or, less commonly, Streptococcus pyogenes. Impetigo may be bullous or nonbullous and typically manifests with honey-colored, crusted lesions with surrounding erythema on the face or, occasionally, the extremities. It can often be diagnosed clinically, but bacterial culture is recommended to identify the causative pathogen. First-line treatment for localized impetigo is a topical antibiotic (e.g., mupirocin), which typically resolves the infection without complications. Systemic antibiotics may be indicated for more widespread disease or to decrease transmission during an outbreak.

• 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
  • S. aureus: majority of cases ^[3]
    • Causes both bullous impetigo and nonbullous impetigo
    • S. aureus strains that produce exfoliative toxins A and B are responsible for bullous impetigo. ^[4][5]
  • S. pyogenes (GAS): causes nonbullous impetigo
  • S. aureus and GAS coinfection may occur
• Predisposing factors ^[3]
  • Warm and humid climate
  • Crowded, unsanitary living conditions
  • Poor personal hygiene
  • Medical conditions
    • Preexisting 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 preexisting skin lesions

• Rare manifestation: ecthyma
  • Ulcerative impetigo that extends into the dermis
  • Manifests with coin-shaped, superficial ulcers with a punched-out appearance and yellow or brown-black crusts
  • May cause scarring because ecthyma involves the deep layers of the skin

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

• Clinical diagnosis based on typical manifestations of impetigo (see also “Differential diagnoses of impetigo”) ^[11]
• Gram stain and culture of pus or exudate: to identify causative pathogens ^[3][11]
• Consider diagnostics for poststreptococcal glomerulonephritis (PSGN) if suspected.

Gram stain and culture are recommended for distinguishing S. aureus and/or GAS as the cause of impetigo; testing is not necessary in patients with typical lesions. ^[11]

See “Differential diagnosis of scaling,” “Blistering skin diseases,” and “SSTIs.” ^[6][12]

• Conditions that cause localized inflammation ^[3]
  • Atopic dermatitis
  • Contact dermatitis
  • Seborrheic dermatitis
  • Cutaneous candidiasis
  • Tinea
  • Herpes simplex virus infection
  • Erysipelas
  • Folliculitis
  • Scabies
• Conditions that cause bullae ^[3]
  • Pemphigus vulgaris and bullous pemphigoid
  • Bullous fixed drug reaction
  • Insect bites or burns
  • Varicella
  • Stevens-Johnson syndrome

The differential diagnoses listed here are not exhaustive.

Topical antibiotics ^[3][13]

• Indications: any form of impetigo with a limited area affected
• Options ^[13]
  • Mupirocin ^[3]
  • Retapamulin ^[3]
  • Ozenoxacin ^[14]
  • Fusidic acid (off-label; not available in the US) ^[3]

Oral antibiotics ^[3]

• Indications ^[3][11]
  • Impetigo with large bullae or widespread involvement
  • Ecthyma
  • Outbreak setting
• Options ^[3][11][15]
  • Targeting both S. aureus and GAS
    • Cephalexin ^[11]
    • Dicloxacillin ^[3][11]
    • Amoxicillin/clavulanate ^[11]
  • Confirmed or suspected MRSA ; ^[11][15]
    • Clindamycin ^[11]
    • TMP/SMX (off-label) ^[11]
    • Doxycycline (off-label) ^[3]
• Duration: usually 7 days

Treatment with penicillin is only recommended if cultures yield GAS alone. Otherwise, avoid treating impetigo with penicillin and macrolides as they are usually ineffective. ^[3][11]

Supportive care ^[3]

Provide patient and guardian education and counseling on:

• Measures to reduce contagion: e.g., wound care, handwashing, contact precautions (see “Prevention”)
• Clinical monitoring for complications (e.g., cellulitis, sepsis, PSGN)

Avoid topical disinfectants (e.g., chlorhexidine) as they are less effective than topical antibiotics. ^[3]

• In GAS infections: acute poststreptococcal glomerulonephritis (PSGN)
• Very rarely: staphylococcal scalded skin syndrome (SSSS)
• Superinfection ^[16]

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.