Impetigo (see also Chapter 16: Superficial Bacterial Infections, Folliculitis, and Hidradenitis Suppurativa) is a superficial bacterial skin infection that can occur in all age groups but is most common among infants and children.

Impetigo is most often caused by S. aureus, or, less often by S. pyogenes (Group A beta-hemolytic Streptococcus, GABHS), although it is often difficult to ascertain the etiologic agent.

Bullous impetigo occurs when there is infection with the exfoliative toxin producing strain of S. aureus.

Impetigo may be transmitted from contact with another child or an infected source.

It often starts at the site of a minor skin injury such as an abrasion, an arthropod bite reaction, or eczema that has been excoriated and can spread via autoinoculation.

Diagnosis can be confirmed by culture of the base of the lesion after removal of the crust or from the intact bullae.

Overall, the majority of cases of impetigo in childhood are the nonbullous form.

Nonbullous impetigo begins as a pink macule or papule followed by a transient vesicle or pustule that evolves into a yellow honey-colored crusted plaque (Fig. 5.1).

In children, nonbullous impetigo tends to occur on the face, especially around the nose and mouth, and also on exposed areas of the body (Fig. 5.2).

The bullous form has a predilection for the area of skin under the diaper and body folds and is the more common form of impetigo in infants.

Bullous impetigo often occurs in the neonatal period but can also occur in children.

Early in bullous impetigo there are small vesicles that can enlarge into 1- to 2-cm superficial flaccid transparent, bullae. Occasionally bullae may be up to 5 cm in diameter. Bullae rupture easily and leave a collarette of scale but typically there is no thick crust or surrounding erythema (Fig. 5.3).

Bullous impetigo can also present as a shallow pink, moist, erosion surrounded by remnants of the blister roof.

Usually there are no associated systemic symptoms but occasionally the bullous form can be associated with weakness, fever, and diarrhea.

Ecthyma (see Fig. 16.5), also called ulcerated nonbullous impetigo, is a deep dermal infection that can result from untreated impetigo, usually caused by S. pyogenes.

In immunodeficient patients, the exfoliative toxin in bullous impetigo may disseminate and cause generalized staphylococcal scalded skin syndrome (see Chapter 7: Viral and Bacterial Exanthems).

Rarely, poststreptococcal glomerulonephritis (but not rheumatic fever) has been reported to follow impetigo caused by certain strains of streptococci.