Impetigo is a bacterial infection of the epidermis caused by Staphylococcus aureus and group A beta-hemolytic streptococci (GABHS). Both organisms may be present at the same time in the affected site. Community-acquired methicillin-resistant S. aureus (CA-MRSA) may cause impetigo. Impetigo is highly infectious and easily transmitted by hand contact. Various types of dermatitis can become secondarily infected with bacteria, and the skin is then called "impetiginized." About 30% of people are colonized in the anterior nares by S. aureus. The bacteria are transmitted from one person to another through hand contact, entering through broken skin created by cutaneous diseases, burns, surgery, trauma, radiation therapy, and insect bites.
Impetigo is a common condition that occurs in all age groups and in both genders equally. The incidence in those younger than 6 years is higher than in adults. Peak incidence occurs during the summer and fall. Most patients recover without complications. Individuals with impetigo from streptococcal infections can develop glomerulonephritis as a rare complication. Impetigo is usually diagnosed clinically based on its characteristic appearance of honey crusts and superficial ulcerations (Figs. 33-36). Exudate from beneath the skin crust should be obtained for culture and sensitivity testing if a community outbreak has occurred, MRSA is suspected, or poststreptococcal glomerulonephritis is present.
Mupirocin ointment is the treatment of choice for small areas of impetigo and is as effective as oral antibiotics, including cases caused by MRSA and GABHS. Mupirocin three times daily for 5 days each month is also recommended intranasally for patients found to be chronic nasal carriers. Oral antibiotics are used in patients with extensive impetigo or with refractory infection. A cephalosporin, semisynthetic
penicillin, or beta-lactam-beta-lactamase inhibitor is recommended. If bacterial cultures reveal MRSA, trimethoprim-sulfamethoxazole, doxycycline (over age 10), or clindamycin are appropriate. Gentle debridement of crusts using antibacterial soap and a washcloth is also recommended. Patients should be encouraged to use careful handwashing to prevent further spread of infection.
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