Impetigo is a common superficial infection of the skin characterized by honey-colored crusts or bullae, typically caused by Staphylococcus aureus, sometimes caused by Streptococcus pyogenes, or both.
Bacterial resistance such as community-acquired methicillin-resistant Staphylococcus aureus (MRSA) is becoming more prevalent; thus, treatment of infections must take evolving resistance patterns into account.
SYNONYMS Bullous impetigo, blistering distal dactylitis, impetigo contagiosa.
AGE Preschool children, young adults.
INCIDENCE Common; up to 10% of dermatology visits.
SEASON Peak summer and fall.
ETIOLOGY Bullous impetigo is most often caused by Staphylococcus aureus phage group II strains which produce exfoliative toxin A or B. Vesiculopustular impetigo is often caused by Staphylococcus aureus or group A β-hemolytic Streptococcus species.
PREDISPOSING FACTORS Colonization of the skin and/or nares of the patient or patient's family members, warm temperatures, high humidity, poor hygiene, atopic diathesis, skin trauma.
Crusted impetigo is caused by S. aureus or occasionally S. pyogenes at sites of skin trauma. Bullous impetigo is caused by an S. aureus exfoliative toxin A, which binds to desmoglein 1, cleaving its extracellular domain, resulting in an intraepidermal blister.
The skin lesions begin as erythematous areas, which may progress to superficial vesicles and bullae that rupture and form honey-colored crusts. The skin lesions are contagious and spread by person-to-person contact or fomites. Systemic symptoms are rare but can include fever and lymphadenopathy.
TYPE Macules, vesicles, bullae, crusts, and erosions (Fig. 20-1).
Blisters and honey-colored crusts on the torso of a young child.
COLOR Pink, yellow “stuck-on” crusts. Pustules may appear whitish-yellow.
ARRANGEMENT Discrete, confluent, or satellite lesions from autoinoculation.
DISTRIBUTION Face, arms, legs, buttocks, distal fingers (Fig. 20-2), toes.
Blistering distal dactylitis
Tense fluid-filled blister on the fingertip of a young boy with S. aureus nasal carriage. (Slide used with permission from Dr. Lisa M. Cohen.)
In the early vesicular stage, impetigo may simulate varicella, herpes simplex, or candidiasis. The bullous stage may be confused with bullous insect bites, autoimmune bullous dermatoses, adverse drug reactions, or burns. The crusted stage may resemble eczematous dermatoses or tinea infections.
DERMATOPATHOLOGY Acantholytic cleft in the stratum ...