impetigo

Introduction

Superficial infection involving the epidermis characterized by crusted erosions or ulcerations.

Etiology

• Staphylococcus aureus
  • most commonly phage group 2, type 71
  • etiologic agent of Staphylococcal scalded skin syndrome same
• Streptococcus pyogenes
• primary infection of superficial break in skin
• secondary infection of pre-exsiting dermatosis
• predisposing factors
  • colonization of skin by S aureus & S pyogenes
  • warm ambient temperature
  • high humidity
  • dermatosis (esp atopic dermatitis)
• precipitating factors
  • insect bite

Epidemiology

• primary infections more common in children
  • most common bacterial infection in chidren
• secondary infections occur at any age
• common disorder, very contagious
• 25% of patients are nasal carriers of S aureus
• acquired by person to person contact

Pathology

• vesicle formation in subcorneal or granular layer
• acantholysis
• spongiosis
• perivascular infiltrate of neutrophils & lymphocytes in dermis
• gram positive cocci within neutrophils in vesicles
• elaboration of S aureus exotoxin (exfoliatin)
  • same toxin causes Staphylococcal scalded skin syndrome

Clinical manifestations

• durations of lesions: days to weeks
• variable pruritus
• non-bullous: small vesicles or pustules rupture resulting in erosions which become crusted
• bullous:
  • vesicles or bullae rupture & decompress
  • with unroofing, erosions form
  • indicates infection with Staphylococcus
• crusts may be gold (honey-colored) to hemorrhagic
  • collarette of scale surrounding rusted erosion
• lesions round or oval, 1-3 cm in size
• scattered, discrete lesions, may be larger confluent lesions
• satellite lesions occur by auto-inoculation
• itchy, raised, weeping patches with scaly borders that develop honey-colored crusts
• distribution:
  • face, arms, legs, buttocks
  • bullous: trunk, face, hands, intertriginous sites
• regional lymphadenopathy may be present

* images

Laboratory

• Gram stain of lesion
  • Gm+ cocci in chains & clusters within neutrophils
• wound culture can be obtained from blister fluid or exudative crust
• complete blood count (CBC): +/- leukocytosis
• serology: anti-DNAse beta indicates prior group A Streptococcal infection
• biopsy

Complications

• also see ecthyma
• non suppurative complications of group A streptococci

Differential diagnosis

• non-bullous impetigo
  • excoriation
  • perioral dermatitis
  • seborrheic dermatitis
  • contact dermatitis
  • Herpes simplex
  • Dermatophytosis
• bullous impetigo
  • contact dermatitis
  • Herpes simplex
    • Herpes gladiatorum, wrestlers
      • clusters of clear fluid-filled vesicles (clustered papules) with surrounding erythema that crust over
  • Herpes zoster
  • folliculitis
  • burns
  • bullous pemphigoid
  • dermatitis herpetiformis
• erysipelas (group A streptococcus)

Management

• wash with soap & water & removal of crusts
• topical agents
  • may be sufficient for limited disease of head & neck
  • topical antibiotic after soaking of crusts
    • mupirocin (Bactroban) TID to affected skin & to nares for 7-10 days
    • bacitracin
  • benzoyl peroxide (prevention)
• systemic antibiotics for more extensive disease
  • Staphylococcus aureus
    • dicloxacillin 250-500 mg PO QID
    • cephalexin
      • 250-500 mg PO QID for 10 days (adults)
      • 40-50 mg/kg/day for 10 days (children)
    • amoxicillin clavulanate (Augmentin)
      • 20 mg/kg/day divided TID for 10 days
    • macrolides for penicillin-sensitive individuals
      • erythromycin
        • 1-2 g/day divided QID for 10 days (adults)
        • 40 mg/kg/day divided QID for 10 days (children)
      • clarithromycin 250-500 mg PO BID for 10 days
      • azithromycin 250 mg QD for 5-7 days
    • clindamycin
      • 150-300 mg QID for 10 days (adults)
      • 15 mg/kg/day divided QID for 10 days (children)
  • methicillin-resistant Staphylococcus aureus (MRSA)
    • mupirocin ointment
    • minocycline 100 mg PO BID for 10 days
      • doxycycline 100 mg PO BID
    • Bactrim DS 1-2 tabs QD
    • ciprofloxacin 500 mg PO BID
  • group A streptococcus (S pyogenes)
    • penicillin VK 250 mg PO TID
    • benzathine penicillin
      • 600,000 units IM (< 6 years of age)
      • 1,200,000 units IM (> 6 years of age)
    • erythromycin 250-500 mg PO QID for 10 days
    • cephalexin 250-500 mg QID for 10 days
• prognosis
  • untreated lesions progress for several weeks & with poor hygiene may form ecthyma
  • most cases resolve spontaneously
  • very contagious
• prevention
  • reoccurence may occur because of failure to erradicate infection or reinfection from family member
  • mupirocin to nares of patient & family members for 5 days
  • benzoyl peroxide soap

More general terms

• bacterial infection
• skin infection
• vesiculobullous dermatitis

Additional terms

• cellulitis
• erysipelas
• Staphylococcal scalded skin syndrome