ESSENTIALS OF DIAGNOSIS
Superficial blisters filled with purulent material that rupture easily.
Crusted superficial erosions.
Positive Gram stain and bacterial culture.
Impetigo is a contagious and autoinoculable infection of the skin (epidermis) caused by staphylococci or streptococci.
The lesions consist of macules, vesicles, bullae, pustules, and honey-colored crusts that when removed leave denuded red areas (Figure 6–17). The face and other exposed parts are most often involved. Ecthyma is a deeper form of impetigo caused by staphylococci or streptococci, with ulceration and scarring (eFigure 6–48) that occurs frequently on the extremities.
Ecthyma, shown here, represents a deeper form of impetigo caused by Staphylococcus aureus or streptococci. (Used, with permission, from S Goldstein, MD.)
Bullous impetigo. (Used, with permission, from Jack Resneck, Sr, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley H. The Color Atlas of Family Medicine, 2nd ed. McGraw-Hill, 2013.)
Gram stain and culture confirm the diagnosis. In temperate climates, most cases are associated with S aureus infection. Streptococcus species are more common in tropical infections.
The main differential diagnoses are acute allergic contact dermatitis (eFigure 6–49) and herpes simplex. Contact dermatitis may be suggested by the history or by linear distribution of the lesions, and culture should be negative for staphylococci and streptococci. Herpes simplex infection usually presents with grouped vesicles or discrete erosions and may be associated with a history of recurrences. Viral cultures are positive.
Poison ivy: fine vesicles in a linear pattern. (Reproduced, with permission, from Bondi EE, Jegasothy BV, Lazarus GS [editors]. Dermatology: Diagnosis & Treatment. Originally published by Appleton & Lange. Copyright © 1991 by The McGraw-Hill Companies, Inc.)
Soaks and scrubbing can be beneficial, especially in unroofing lakes of pus under thick crusts. Topical agents, such as bacitracin, mupirocin, and retapamulin, are first-line treatment options for infections limited to small areas. In widespread cases, or in immunosuppressed individuals, systemic antibiotics are indicated. Cephalexin, 250 mg orally four times daily, is usually effective. Doxycycline, 100 mg orally twice daily, is a reasonable alternative. Community-associated methicillin-resistant S aureus (CA-MRSA) may cause impetigo, and initial coverage for MRSA could include doxycycline (100 mg orally twice daily) or trimethoprim-sulfamethoxazole (TMP-SMZ, double-strength tablet orally twice daily). About 50% of CA-MRSA cases are quinolone resistant. Recurrent impetigo is associated with nasal carriage of S aureus and is treated with ...