• Bullous: always Staphylococcus aureus
• Nonbullous: still predominantly S. aureus, but may also be group A b-hemolytic streptococcus and miscellaneous anaerobes
• Associated illnesses: varicella, tinea capitis/corporis, scabies, contact dermatitis, eczema
• Predisposing conditions: warm temperature, high humidity, prior antibiotic use (altering normal skin flora), and altered host immunity (e.g., IgA deficiency and defect in cellular immune system)
• Factors that expose fibronectin receptors in the skin, enhancing bacterial binding: underlying skin disease (atopic dermatitis, fungal skin infections), minor trauma (scratches, insect bites, burns)

• Organisms colonize the skin surface and then invade superficially in areas of minor trauma (e.g., an insect bite). Bacteria are transferred from a colonized area (under the fingernails) to the another area (e.g., the nares).
• Microscopic findings: vesicle formation in the subcorneal or granular region with acantholytic cells, spongiosis, edema of the papillary dermis, infiltration of lymphocytes and neutrophils around the blood vessels (the nonbullous form will have little or no vesicle formation)

• Most common in warm, humid areas
• Most common in warm, humid seasons
• Associated with socioeconomic disadvantage, especially crowding
• Most common bacterial skin infection in children; bacterial skin infections account for up to 17% of clinical visits.
• Rare under 2 years of age; most common between 2 and 7 years of age; seen in older groups more often as part of an epidemic

• Suppurative
  • Cellulitis
  • Lymphadenitis
  • Osteomyelitis
  • Pyogenic arthritis
  • Pneumonia
  • Sepsis
• Nonsuppurative
  • Toxic shock syndrome
  • Scarlet fever
  • Acute poststreptococcal glomerulonephritis

• Lesions left untreated resolve spontaneously in most cases.
• Treatment primarily prevents spread and speeds healing.
• Unless there is extension of infection beyond impetigo to cellulitis or abscess (uncommon), the infection is superficial and there is no scarring.

• Varicella
• Eczema herpetiformis
• Staph scalded-skin syndrome
• Tinea corporis
• Scabies
• Contact dermatitis
• Numnular eczema
• Linear IgA bullous dermatosis
• Burns (thermal and chemical)

• Systemic symptoms are rare.
• Bullous impetigo develops in previously untraumatized skin.
• Nonbullous impetigo is frequently associated with predisposing mild trauma.

• Bullous: transparent bullae that rupture easily, leaving a rim surrounding a shallow ulcer; normal surrounding skin; regional adenopathy rare
• Nonbullous: papule or vesicle progression to a honey-crusted plaque; erythema of surrounding skin; regional adenopathy common

• None needed in most cases: clinical diagnosis
• Gram stain and culture are indicated for recurrent or systemic illness; obtain needle aspirate from bulla or by “unroofing” crust and obtaining sample of the purulent material beneath. If positive, it may represent colonization rather than infection; it should be used to identify the organism, not to make a diagnosis.
• CBC: in the presence of systemic symptoms
• Blood culture: in the presence of systemic symptoms
• A skin biopsy may be indicated if diagnosis is in question

• Antibiotic resistance patterns in the community will guide choice of antibiotic.
• Most community-acquired cases S. aureus are not methicillin-resistant but may occur in households with IV drug users or in someone who works or lives in a nursing home.
• Many infections, even with organisms resistant in vitro, will still have a good clinical response.
• Topical treatment with mupirocin (Bactroban) three times per day for 7 days will not prevent nonsuppurative complications and is not appropriate when lesions are extensive, around the mouth, or there is propylene glycol hypersensitivity. Cream is preferred over the ointment unless there is so much crusting that the cream will not penetrate.
• Other topical antibacterials (bacitracin, polysporin) are not effective.
• Oral agents should be used when topical agents are contraindicated or when compliance with a topical agent is doubtful:
  • First line: cephalexin 50 mg/kg/d in two divided doses or erythromycin ethylsuccinate 50 mg/kg/d in three to four divided doses for 7 to 10 days (compliance with cephalexin is better because of erythromycin gastrointestinal side effects)
  • Second line: dicloxacillin 50 mg/kg/d (very effective, but unpalatable in liquid form), amoxicillin/clavulanic acid 40 mg/kg/d (very effective, with high cost and higher incidence of gastrointestinal side effects); clindamycin 15 mg/kg/d (very effective, but with greatest alteration of GI flora), azithromycin (very effective and fewer days [only 5 days] of dosing, but with higher cost), extended-spectrum cephalosporins (probably no more effective than first-generation, but at higher cost)
• Failed treatment: Add rifampin 20 mg/kg/d and use muciprocin in nose to decrease staph carriage

• Nonbullous: If untreated, lesions progress slowly over several weeks and then heal spontaneously; occasionally ulcer forms, even when properly treated.
• Bullous: They usually rupture spontaneously (based on size and body location) and then heal over a period of several days to 1 week when properly treated.

• Surrounding skin, for development of deeper infection with abscess or cellulitis
• Fever is unusual and should prompt investigation for deeper infection or another cause.
• Recurrence suggests an S. aureus carrier state or inadequate initial therapy.

• Patient/school education (handwashing of paramount importance): very contagious; spread throughout household not unusual; easily spread via physical contact and fomites, especially on athletic teams
• Trim fingernails to prevent scratching; use gloves at night.
• Separate sleeping quarters and clothing until lesions resolved
• Treat underlying (predisposing) skin diseases and infestations.

• Spread throughout a household is not uncommon, with children frequently reinfecting themselves and other family members. Children with underlying skin disease (e.g., eczema) are difficult to treat because of heavy bacterial skin colonization and mechanical trauma to skin associated with itching.
• When cultures reveal both staph and strep, there is no way to determine which is causing the infection; both must be treated empirically.

Q: How do you make a decision to treat topically or systemically?
A: Many factors influence this decision. It is impractical to treat a large number of lesions topically, and it is “overkill” to treat a few small lesions with a systemic course of antibiotics. Individual therapy should be tailored to the number and extent of lesions, caregivers’ preference for type of therapy, and prior experience with infections in this patient.

Q: What should be done with a patient who continues to have impetigo despite repeated courses of antibiotics?
A: A search for a household source who is reinfecting the patient is probably most important. Culture with sensitivities should be performed to determine if treatment is adequate, but in most cases this is not the problem. Eliminating patient carriage of the organism (with rifampin and mupirocin) should be considered. Underlying skin diseases and irritants should be eliminated if possible. Other diagnoses should be entertained in the truly recalcitrant cases.

Q: Should the child be isolated from other family members and kept from school?
A: Until the lesions are treated, close contact of the child with other people should be discouraged through both sleeping and play.

Q: What is the difference between mupirocin cream and ointment?
A: The cream with a water base will be absorbed into the skin at a higher concentration in most cases and therefore be more effective. However, if there is significant crusting, the ointment with its oil base may penetrate better.

Bass JW, Chan DS, Creamer KM, et al. Comparison of oral cephalexin, topical mupirocin, and topical bacitracin for treatment of impetigo. Pediatr Infect Dis J 1997; 16(7):708–710.

Dagan R. Impetigo in childhood: changing epidemiology and new treatments. Pediatr Ann 1993; 22(4):235–240.

Sadick NS. Current aspects of bacterial infections of the skin. Dermatol Clin 1997; 15(2):341–349.

Scales JW, Fleischer AB, Krowchuk DP. Bullous impetigo. Arch Pediatr Adolesc Med 1997; 151(11):1168–1169.