ESSENTIALS OF DIAGNOSIS
Nonbullous: yellowish crusted plaques.
Bullous: bullae, with minimal surrounding erythema, rupture to leave a shallow ulcer.
Impetigo is a bacterial infection of the skin. More than 70% of cases are of the nonbullous variety.
Most cases of nonbullous impetigo are caused by Staphylococcus aureus, although group A β-hemolytic streptococci are found in some cases. Coagulase-positive S. aureus is the cause of bullous impetigo; methicillin-resistant S. aureus (MRSA) has been isolated from patients. Impetigo can develop in traumatized skin, or the bacteria can spread to intact skin from its reservoir in the nose.
Nonbullous impetigo usually starts as a small vesicle or pustule, followed by the classic small (<2-cm) honey-colored crusted plaque. The infection may be spread to other parts of the body by fingers or clothing. There is usually little surrounding erythema, itching occurs occasionally, and pain is usually absent. Regional lymphadenopathy is seen in most patients. Without treatment, the lesions resolve without scarring in 2 weeks.
Bullous impetigo is usually seen in infants and young children. Lesions begin on intact skin on almost any part of the body. Flaccid, thin-roofed vesicles develop, which rupture to form shallow ulcers.
Nonbullous impetigo is unique in appearance. Bullous impetigo is similar in appearance to pemphigus and bullous pemphigoid. Growth of staphylococci from fluid in a bulla confirms the diagnosis.
Cellulitis follows ~10% of cases of nonbullous impetigo but rarely follows bullous impetigo. Either type may rarely lead to septicemia, septic arthritis, or osteomyelitis. Scarlet fever and poststreptococcal glomerulonephritis, but not rheumatic fever, may follow streptococcal impetigo.
Localized disease is effectively treated with mupirocin ointment. Topical 1% retapamulin ointment is a newer, second-line option. Patients with widespread lesions or evidence of cellulitis should be treated with systemic antibiotics effective against staphylococci and streptococci. If infection with MRSA is a possibility, trimethoprim-sulfamethoxazole should be considered where community-acquired MRSA is a likely cause, while intravenous vancomycin is the preferred drug for hospitalized patients.
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Fungal infections of the skin and skin structures may be generally grouped into three categories: dermatophyte infections, other tinea infections, and candidal infections.
Dermatophytoses are caused by a group of related fungal species—primarily Microsporum, Trichophyton, and Epidermophyton—that require keratin for growth and can invade hair, nails, and the stratum corneum of the skin. Some of these organisms are spread from person to person; some are zoonotic, spreading from animals to people; and some infect people from the soil. Other fungi can also cause skin disease, such as Malassezia furfur in tinea versicolor. Finally, Candida albicans, a common resident of the gastrointestinal tract, can cause diaper dermatitis and thrush.