Non-bullous impetigo is a highly contagious superficial skin infection primarily caused by Staphylococcus aureus in industrialized countries. However, group A streptococcus (Streptococcus pyogenes) remains a common cause of non-bullous impetigo in developing countries. It has a predilection for children and is the most common cause of bacterial infection in this age group. 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.

Although methicillin-resistant S. aureus (MRSA) infection of the skin usually presents as recurrent furunculosis or skin abscesses, MRSA has been shown to cause impetigo. 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.

Immunocompromised Patient Considerations:
Pyodermas (cutaneous bacterial infections) including impetigo are quite common in human immunodeficiency virus (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.