Impetigo

Published on 19/03/2015 by admin

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Last modified 19/03/2015

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Impetigo

Robert M. Burd and Michael Sladden

Evidence Levels:  A Double-blind study  B Clinical trial ≥ 20 subjects  C Clinical trial < 20 subjects  D Series ≥ 5 subjects  E Anecdotal case reports

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Impetigo is a superficial bacterial infection of the skin. The most common pathogen is Staphylococcus aureus, although β-hemolytic streptococci may also be implicated. The infection is highly contagious and can easily spread to other body sites or close contacts.

Impetigo may be primary, with direct bacterial invasion of previously normal skin, or secondary, where infection develops due to an underlying skin disease, such as scabies or eczema, disrupting the skin barrier.

Impetigo is classified as bullous or non-bullous. In the more common non-bullous form, thin-walled vesicles rupture to form superficial erosions with yellowish-brown crusts, which eventually heal without scarring. Bullous impetigo is characterized by larger bullae or blisters, which may continue to develop for several days.

Management strategy

The main aim of treatment is to eradicate the infecting bacteria to allow rapid healing of skin lesions and control the spread of infection. This requires the use of an appropriate antimicrobial delivered in an effective manner. Antibiotics may be administered either orally or topically. The choice between topical or oral therapy depends on:

In Europe, S. aureus has been recognized as the major pathogen in both bullous and non-bullous impetigo. Traditionally, in the US, non-bullous impetigo was considered to be caused primarily by streptococci, but recent evidence indicates that S. aureus is now the most common pathogen in both forms of impetigo in the US as well.

Oral or topical antibiotics with proven efficacy against S. aureus are the first choice of therapy. It is reasonable to use short courses of topical antibiotics for mild, limited impetigo, while reserving oral antibiotics for recalcitrant, extensive, systemic disease.

Globally, the majority of isolates of S. aureus are resistant to penicillin. Erythromycin resistance is also becoming more prevalent.

In developing countries, where impetigo causes a significant burden of disease, streptococcus is often the predominant pathogen. In these countries, topical agents are expensive and may be unavailable. Treatment strategies have to be sufficiently flexible to meet local needs.

Historically, topical treatment of impetigo was ineffective due to the emergence of bacterial resistance to tetracyclines and gentamicin, and problematic because of contact sensitivity to topical antimicrobials. More recently introduced topical antibiotics are as effective as traditional oral antibiotics. When used in courses of less than 2 weeks, bacterial resistance does not appear to be a major problem. However, bacterial resistance patterns vary with geographical location, and treatment should be influenced by local data and expertise.

Recent studies of retapamulin, a pleuromutilin antibacterial developed for topical use, indicate that it is effective and safe in the treatment of primary impetigo.

Strains of bacteria causing impetigo are often extremely virulent. Patients therefore need to be educated on personal hygiene methods to avoid the spread of infection. The use of topical antiseptics and soaks to remove dried exudate and crusts has not been shown to be of benefit. Evidence regarding the value of disinfecting measures is limited. However, common sense would indicate that cleaning lesional skin with soap and water or a mild, non-irritant antiseptic will aid the application of topical antibiotics and reduce the spread of infection.

Nasal carriage of S. aureus occurs in a high proportion of both patients and asymptomatic family members. Therefore, in recurrent cases or multiple familial cases, treatment of nasal and pharyngeal carriage may be necessary.

Increasingly, methicillin-resistant S. aureus (MRSA) has become an important cause of impetigo. MRSA poses a challenge because of its enhanced virulence and resistance to standard antibiotic therapy. Antibiotic treatment should be guided by the likely causative agent and knowledge of local resistance patterns, as well as bacterial susceptibility testing.

Specific investigations

A Gram stain of a swab from the lesion or exudate will reveal Gram positive cocci, confirming the clinical diagnosis. Bacterial culture and sensitivity from a pretreatment swab is useful to assess suitable alternative antibiotics in cases that do not respond to conventional treatment.