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Impetigo and Ecthyma


Wingfield E. Rehmus

, MD, MPH, University of British Columbia

Last full review/revision Feb 2021| Content last modified Feb 2021
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Impetigo is a superficial skin infection with crusting or bullae caused by streptococci, staphylococci, or both. Ecthyma is an ulcerative form of impetigo. Diagnosis is clinical. Treatment is with topical and sometimes oral antibiotics.

No predisposing lesion is identified in most patients, but impetigo may follow any type of break in the skin. General risk factors seem to be a moist environment, poor hygiene, or chronic nasopharyngeal carriage of staphylococci or streptococci. Impetigo may be bullous or nonbullous. Staphylococcus aureus is the predominant cause of nonbullous impetigo and the cause of all bullous impetigo. Bullae are caused by exfoliative toxin produced by staphylococci. Methicillin-resistant S. aureus (MRSA) has been isolated in about 20% of recent cases of impetigo.

Symptoms and Signs of Impetigo and Ecthyma

Nonbullous impetigo typically manifests as clusters of vesicles or pustules that rupture and develop a honey-colored crust (exudate from the lesion base) over the lesions. Smaller lesions may coalesce into larger crusted plaques.

Bullous impetigo is similar except that vesicles typically enlarge rapidly to form bullae. The bullae burst and expose larger bases, which become covered with honey-colored varnish or crust.

Examples of Nonbullous and Bullous Impetigo

Ecthyma is characterized by small, purulent, shallow, punched-out ulcers with thick, brown-black crusts and surrounding erythema.

Impetigo and ecthyma cause mild pain or discomfort. Pruritus is common; scratching may spread infection, inoculating adjacent and nonadjacent skin.

Diagnosis of Impetigo and Ecthyma

  • Clinical evaluation

Diagnosis of impetigo and ecthyma is by characteristic appearance.

Cultures of lesions are indicated only when the patient does not respond to empiric therapy. Patients with recurrent impetigo should have nasal culture. Persistent infections should be cultured to identify MRSA.

Treatment of Impetigo and Ecthyma

  • Topical mupirocin, retapamulin, fusidic acid, or ozenoxacin

  • Sometimes oral antibiotics

The affected area should be washed gently with soap and water several times a day to remove any crusts.

Treatment for localized impetigo is topical mupirocin antibiotic ointment 3 times a day for 7 days, retapamulin ointment 2 times a day for 5 days, or ozenoxacin 1% cream applied every 12 hours for 5 days. Fusidic acid 2% cream 3 to 4 times a day until lesions resolve is as effective but is not available in the US.

Oral antibiotics (eg, dicloxacillin or cephalexin 250 to 500 mg 4 times a day [12.5 mg/kg 4 times a day for children] for 10 days) may be needed in immunocompromised patients, those with extensive or resistant impetigo lesions, or for ecthyma; clindamycin 300 mg every 6 hours or erythromycin 250 mg every 6 hours may be used in penicillin-allergic patients, but resistance to both drugs is an increasing problem.

Use of initial empiric therapy against MRSA MRSA and purulent or complicated cellulitis Cellulitis is acute bacterial infection of the skin and subcutaneous tissue most often caused by streptococci or staphylococci. Symptoms and signs are pain, warmth, rapidly spreading erythema... read more MRSA and purulent or complicated cellulitis is not typically advised unless there is compelling clinical evidence (eg, contact with a person who has a documented case, exposure to a documented outbreak, culture-documented local prevalence of > 10% or 15%). Treatment of MRSA should be directed by culture and sensitivity test results; typically, clindamycin, trimethoprim/sulfamethoxazole, and doxycycline are effective against most strains of community-associated MRSA.

Prompt recovery usually follows timely treatment. Delay can cause cellulitis, lymphangitis, furunculosis, and hyperpigmentation or hypopigmentation with or without scarring. Children aged 2 to 4 years are at risk of acute glomerulonephritis if nephritogenic strains of group A streptococci are involved (types 49, 55, 57, and 59); nephritis seems to be more common in the southern US than in other regions. It is unlikely that treatment with antibiotics prevents poststreptococcal glomerulonephritis.

Key Points

  • S. aureus causes most nonbullous impetigo and all bullous impetigo.

  • Honey-colored crust is characteristic of bullous and nonbullous impetigo.

  • For persistent impetigo, culture the wound (to identify methicillin-resistant S. aureus [MRSA]) and the nose (to identify a causative nasal reservoir).

  • Treat most cases with topical antibiotics.

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