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Impetigo
Elisabeth L. Backer, MD
image BASICS
DESCRIPTION
  • A contagious, superficial, intraepidermal infection occurring prominently on exposed areas of the face and extremities, most often seen in children
  • Infected patients usually have multiple lesions.
  • Cultures are positive in >80% cases for Staphylococcus aureus either alone or combined with group A &bgr;-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 golden appearance; local lymphadenopathy may occur.
  • Bullous impetigo: staphylococcal impetigo that progresses rapidly from small to large flaccid bullae (newborns/young children) caused by epidermolytic toxin release; 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; fox impetigo
EPIDEMIOLOGY
Incidence
  • Predominant sex: male = female
  • Predominant age: children ages 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
  • &bgr;-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 20 years.
  • 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
  • Possibly tobacco exposure
  • Carriage of group A Streptococcus and Staphylococcus 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
image DIAGNOSIS
PHYSICAL EXAM
  • Tender red macules or papules as early lesions (contact dermatitis presents with pruritic lesions)
  • Thin-roofed vesicles to bullae: usually nontender
  • Pustules
  • Weeping, shallow, red ulcers
  • Honey-colored crusts
  • Satellite lesions
  • Often multiple sites
  • Bullae on buttocks, trunk, face
DIFFERENTIAL DIAGNOSIS
  • Nonbullous
    • Contact dermatitis
    • Chickenpox
    • Herpes
    • Folliculitis
    • Erysipelas
    • Insect bites
    • Severe eczematous dermatitis
    • Scabies
    • Tinea corporis
  • Bullous
    • Burns
    • Pemphigus vulgaris
    • Bullous pemphigoid
  • Stevens-Johnson syndrome
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
  • None usually done; cultures of pus/bullae fluid may be helpful if no response to empiric therapy.
    • Culture: taken from the base of lesion after removal of crust will grow both staphylococci and group A streptococci
    • Antistreptolysin-O (ASO) titer: can be weak positive for streptococci but overall not useful
    • Antideoxyribonuclease B (anti-DNase B) and antihyaluronidase (AHT) response more reliable than ASO response
    • Streptozyme: positive for streptococci
  • Disorders that may alter lab results: Streptococcal pharyngitis will alter streptococcal enzyme tests.
Follow-Up Tests & Special Considerations
  • Monitor for spread of disease and systemic manifestations.
  • Serologic testing is helpful in context of impetigo with subsequent poststreptococcal glomerulonephritis.
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image TREATMENT
GENERAL MEASURES
  • Treatment speeds healing and avoids spread of disease.
  • Prevent with mupirocin or triple antibiotic ointment TID to sites of minor skin trauma.
  • Remove crusts; clean with gentle washing 2 to 3 times daily; and clean with antibacterial soap, chlorhexidine, or Betadine.
  • Washing of entire body may prevent recurrence at distant sites.
MEDICATION
  • In 2005, the Infectious Diseases Society of America (IDSA) recommended topical treatment for limited lesions and oral medication when the disease is more severe/extensive (1)[A].
  • Optimal treatment is unclear due to limited quality of evidence. Treatment reduces spread of infection and enhances resolution (2)[C].
  • Penicillin and macrolide therapy is no longer recommended. Fluoroquinolones are not indicated due to resistance patterns.
  • Consult the local hospital or health department for microbial resistance information.
  • Nonbullous (minor spread, treat 7 days; widespread, treat 10 days); bullous (treat 10 days)
    • Retapamulin 1% ointment to be applied BID for 5 days
    • Mupirocin (Bactroban) 2% topical ointment applied TID for 5 to 7 days (nonbullous only); not as effective on scalp as around mouth
    • Dicloxacillin: adult 250 mg PO QID; pediatric <40 kg: 12 to 25 mg/kg/day divided q6h; >40 kg: 125 to 250 q6h
  • Dicloxacillin, cephalexin, topical mupirocin, and fusidic acid are effective unless local staphylococcal strains are resistant. (For methicillin-resistant S. aureus [MRSA] infections, treatment options include clindamycin, tetracyclines, or trimethoprimsulfamethoxazole.) Oral doses given for 7 days are usually sufficient (3)[C].
  • 1st-generation cephalosporins
    • Children
      • Cephalexin 25 to 50 mg/kg/day divided, q6-12h
      • Cefaclor 20 to 40 mg/kg/day divided q8h
      • Cephradine 25 to 50 mg/kg/day divided q6-12h
      • Cefadroxil 30 mg/kg/day divided BID
    • Adults
      • Cephalexin 250 mg up to QID
      • Cefaclor 250 mg TID
      • Cephradine 500 mg BID
      • Cefadroxil 1 g/day in divided doses
  • Clindamycin 300 mg q6-8h
  • Severe bullous disease may require IV therapy such as nafcillin or cefazolin.
ISSUES FOR REFERRAL
If resistant or extensive infections occur, especially in immunocompromised patients
ADDITIONAL THERAPIES
Monitor for microbial resistance patterns.
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
  • Athletes are restricted from contact sports.
  • School and daycare contagious restrictions
  • Children can return to school 24 hours after initiation of antimicrobial treatment.
Patient Monitoring
If not clear within 7 to 10 days, culture the lesions.
PATIENT EDUCATION
Avoidance of infection spread is the key; hand washing is vital, especially for reducing spread in children.
PROGNOSIS
  • Complete resolution in 7 to 10 days with treatment
  • Antibiotic treatment will not prevent or halt glomerulonephritis, as it will rheumatic fever.
  • If not clear within 7 to 10 days, culture is necessary to find resistant organism.
  • Recurrent impetigo: Evaluate for carriage of S. aureus in nares (also perineum, axillae, toe web). Apply mupirocin ointment to nares BID for 5 days for clearance/decolonization.
REFERENCES
1. Koning S, van der Sande R, Verhagen AP, et al. Interventions for impetigo. Cochrane Database Syst Rev. 2012;(1):CD003261.
2. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft-tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis. 2014;59(2):147-159.
3. Del Giudice P, Hubiche P. Community-associated methicillin-resistant Staphylococcus aureus and impetigo. Br J Dermatol. 2010;162(4):905.
Additional Reading
&NA;
  • George A, Rubin G. A systematic review and metaanalysis of treatments for impetigo. Br J Gen Pract. 2003;53(491):480-487.
  • Parish LC, Jorizzo JL, Breton JJ, et al. Topical retapamulin ointment (1%, wt/wt) twice daily for 5 days versus oral cephalexin twice daily for 10 days in the treatment of secondarily infected dermatitis: results of a randomized controlled trial. J Am Acad Dermatol. 2006;55(6):1003-1013.
  • Stanley JR, Amagai M. Pemphigus, bullous impetigo, and the staphylococcal scalded-skin syndrome. N Engl J Med. 2006;355(17):1800-1810.
See Also
&NA;
Algorithm: Rash, Focal
Codes
&NA;
ICD10
  • L01.00 Impetigo, unspecified
  • L01.01 Non-bullous impetigo
  • L01.03 Bullous impetigo
Clinical Pearls
&NA;
  • Superficial, intraepidermal infection
  • Predominantly staphylococcal in origin
  • Microbial resistance patterns need to be monitored.
  • Topical treatment is recommended for limited lesions and oral medication only when the disease is more severe/extensive.