Impetigo is a common superficial infection of the skin characterized
by honey-colored crusts or bullae, typically caused by S. 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; 10% of
Season Peak summer and fall.
Etiology Bullous impetigo is caused
by phage group II Streptococcus. Vesiculopustular impetigo is caused by
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 Streptococcus
pyogenes at sites of skin trauma. Bullous impetigo is caused by
a S. aureus exfoliative toxin, which binds to desmoglein I, 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
Type Macules, vesicles, bullae,
crusts, and erosions (Fig. 20-1).
FIGURE 20-1 Graphic Jump Location
Impetigo, bullous Blisters
and honey-colored crusts around the umbilicus and diaper area in
Color Pink, yellow “stuck-on” crusts.
Arrangement Discrete, confluent,
or satellite lesions from autoinoculation.
Distribution Face, arms, legs,
buttocks, distal fingers (Fig. 20-2), toes.
FIGURE 20-2 Graphic Jump Location
Blistering distal dactylitis Tense
fluid-filled blister on the fingertip of a young boy with S. aureus
nasal carriage. (Slide courtesy of 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, or burns.
The crusted stage may resemble eczematous dermatoses or tinea infections.
Dermatopathology Acantholytic cleft
in the stratum granulosum with leukocytes and may show scattered
gram-positive cocci. Bacteria are not present within the blister
cavity of bullous lesions.