Nonbullous impetigo is a highly contagious superficial skin infection. It is primarily caused by Staphylococcus aureus in industrialized countries. However, group A streptococcus (Streptococcus pyogenes) remains a common cause of nonbullous impetigo in developing countries. In temperate climates, S aureus causes 90%-95% of cases, and S pyogenes or a combination of both S aureus and S pyogenes account for 5%-10% of cases.

Nonbullous impetigo has a predilection for children, affecting around 12% of children, compared to affecting about 5% of adults globally. Impetigo in adults usually results from extensive close contact with infected children or dermatologic conditions that predispose to superficial infection, such as minor trauma, atopic dermatitis, or infestation (eg, scabies). Small epidemics can occur in crowded environments, such as army barracks.

Clinically, impetigo presents as erythematous vesicles and/or pustules that quickly transition into superficial erosions with a characteristic "honey-colored" crust. Lesions are most commonly seen on the face (eg, around the nose and mouth) and extremities. With the exception of mild lymphadenopathy, patients with impetigo generally have no associated systemic symptoms.

Approximately 50% of patients with nonbullous impetigo will experience recurrent episodes within 12 months and require repeated courses of antibiotics.

Although MRSA infection of the skin usually presents as recurrent furunculosis or skin abscesses, MRSA has been shown to cause impetigo in 1%-10% of cases. Culture and sensitivities should always be performed in patients with lesions suspicious for cutaneous infection, and empiric coverage for MRSA should be instituted if clinical suspicion is high.

An infrequent complication of impetigo is acute poststreptococcal glomerulonephritis (APSG), which is caused by particular serotypes of S pyogenes that are nephritogenic. The risk of APSG is not reduced when antibiotic treatment is administered. Importantly, acute rheumatic fever has not been associated with impetigo.

Immunocompromised Patient Considerations:
Pyodermas (cutaneous bacterial infections) including impetigo are quite common in HIV-infected patients. Additionally, pyodermas are found in immunosuppressed transplant patients, especially in the first months following transplant.

Recurrent bouts of impetigo are more common in immunocompromised patients. This may be due to persistent nasal carriage of Staphylococcus, which has been reported to be as high as 50% in patients with HIV infection.