Impetigo

Description

• A contagious, superficial, intraepidermal infection occurring prominently on exposed areas of the face and extremities, most often seen in children
• Primary impetigo (pyoderma): invasion of previously normal skin
• Secondary impetigo (impetiginization): invasion at sites of minor trauma (abrasions, insect bites, underlying eczema)
• Infected patients usually have multiple lesions.
• Cultures are positive in >80% cases for Staphylococcus aureus either alone or combined with group A β-hemolytic streptococci; S. aureus is the more common pathogen since the 1990s.
• Nonbullous impetigo: most common form of impetigo; formation of vesiculopustules that rupture, leading to crusting with a characteristic of golden appearance; local lymphadenopathy may occur.
• Bullous impetigo: staphylococcal impetigo that progresses from small to large flaccid bullae (newborns/young children) caused by epidermolytic toxin release; ruptured bullae leaving brown crust; less lymphadenopathy; trunk more often affected; <30% of patients
• Folliculitis: considered by some to be S. aureus impetigo of hair follicles
• Ecthyma: a deeper, ulcerated impetigo infection often with lymphadenitis
• System(s) affected: skin/exocrine
• Synonym(s): pyoderma; impetigo contagiosa; impetigo vulgaris

Epidemiology

Incidence

• Predominant sex: male = female
• Predominant age: children aged 2 to 5 years

Prevalence
In the United States: not reported but common

Pediatric Considerations

• Poststreptococcal glomerulonephritis may follow impetigo (in young children).
• Impetigo neonatorum may occur due to nursery contamination.

Etiology and Pathophysiology

• Coagulase-positive staphylococci: pure culture ~50–90%; more contagious via contact
• β-Hemolytic streptococci: pure culture only ~10% of the time (primarily group A)
• Mixed infections of streptococci and staphylococci are common; data suggest increasing importance of staphylococci over the past decades.
• Methicillin-resistant S. aureus (MRSA) detected in some cases
• Direct contact or insect vector
• Can result from contamination at trauma site
• Regional lymphadenopathy

Risk Factors

• Warm, humid environment
• Tropical or subtropical climate
• Summer or fall season
• Minor trauma, insect bites, breaches in skin
• Poor hygiene, poverty, crowding, epidemics, wartime
• Familial spread
• Poor health with anemia and malnutrition
• Complication of pediculosis, scabies, chickenpox, eczema/atopic dermatitis
• Contact dermatitis (Rhus spp.)
• Burns
• Contact sports
• Children in daycare
• Carriage of group A Streptococcus and S. aureus

General Prevention

• Close attention to family hygiene, particularly hand washing among children
• Covering of wounds
• Avoidance of crowding and sharing of personal items
• Treatment of atopic dermatitis

Commonly Associated Conditions

• Malnutrition and anemia
• Crowded living conditions
• Poor hygiene
• Neglected minor trauma
• Any chronic/underlying dermatitis
• Can occur as coinfection with scabies