Impetigo is a common superficial bacterial infection of the skin, which is most often seen in children and is contagious. There are bullous and non-bullous forms.

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What causes it?

Impetigo is caused by several bacteria, most commonly Staphylococcus aureus or Streptococcus pyogenes. The infection often starts where there is a break in the skin such as a bite, scrape, cut or area affected by eczema; however, once it starts, it can spread to adjacent areas with intact skin. It is contagious and can be spread from person to person quite easily.

What does it look like?

Impetigo is characterized by a honey-coloured crust on the surface of the skin. The areas are usually red and open underneath and covered with the yellowish crust on the surface. The lesions can develop on any part of the body but are most common on exposed surfaces such as the arms, legs, and face. Sometimes impetigo develops with blisters. These rupture and leave a ring (collarette) of scale at the border. This form of impetigo is called bullous impetigo and is almost always caused by S. aureus. It can be commonly seen in the diaper area as well as on exposed surfaces as in non-bullous impetigo.

How is it diagnosed?

Lesions with classic honey-crusting can often be diagnosed clinically. Swabs for culture and sensitivity can be performed, particularly if there are risk factors for methicillin-resistant S. aureus (MRSA). If impetigo is suspected, treatment should not be delayed while waiting for results to become available.

How is it treated?  

Impetigo is generally treated with oral antibiotics (cephalexin, erythromycin, dicloxacillin, or clindamycin). Soaks with warm soapy water or in bath water with 1/4 cup of bleach added to the tub can cut down on spreading and help to heal the lesions (see Appendix for instructions on bleach baths). Topical antibiotics such as bacitracin, polymyxin, erythromycin, neomycin, mupirocin or fusidic acid are helpful for very localized disease, but are usually not sufficient for more extensive disease. Treatment continues for 7-10 days.

MSSA / S. pyogenes

Cephalexin:

• Adults – 250-500 mg PO QID
• Pediatrics – 15mg/kg/dose PO TID to QID (max 4g/day) 

Some patients carry S. aureus in the nose or perianal area and develop recurrent infections on their skin as a result. In these cases, treatment of the nostrils and perianal area with mupirocin ointment twice a day for 2 weeks along with use of antibacterial soaps and general house cleaning can cut down on recurrences.

Are there any complications?

Yes, if the impetigo is caused by S. pyogenes the patient is at risk of developing either scarlet fever or post-streptococcal glomerulonephritis. Unfortunately, neither of these conditions seems to be prevented by appropriate antibiotic therapy for the impetigo.  Today, more patients are developing skin infections caused by MRSA. Treatment is frequently with clindamycin, trimethoprim-sulfamethoxazole (Septra), or doxycyline and can be guided by susceptibilities obtained from swabs. 

MRSA

Clindamycin:

• Adults: 150-450 mg PO q6h.
• Pediatrics: 30-40 mg/kg/day PO div q6-8h