Impetigo

Aka: Impetigo, NonBullous Impetigo, Streptococcal Impetigo, Staphylococcal Impetigo, Common Impetigo

1. See Also
   1. Bullous Impetigo
2. Epidemiology
   1. Preschool children most often affected
   2. Most common bacterial Skin Infection in children
   3. Highly contagious
      1. Spreads across body with scratching (autoinoculation)
      2. Spreads easily in daycares and schools
3. Causes
   1. Staphylococcus aureus (most common)
   2. Group A Streptococcus
4. Predisposing factors
   1. Minor Skin Trauma (e.g. abrasions)
   2. Hot, humid weather
   3. Poor hygiene
   4. Daycare attendence
   5. Over-crowded living conditions
   6. Comorbid conditions
   7. Malnutrition
   8. Atopic Dermatitis
   9. Dialysis
5. Types
   1. Bullous Impetigo (less common)
      1. Staphylococcal toxin mediated reaction
   2. NonBullous Impetigo (>70%): Described below
      1. Host response to infection
      2. Primary Impetigo (most common)
         1. Due to direct spread of infection
      3. Secondary Impetigo (Common Impetigo)
         1. Related to underlying secondary Impetigo cause
            1. Diabetes Mellitus
            2. AIDS
            3. Herpes Simplex Virus
            4. Varicella
            5. Insect Bites
6. Symptoms
   1. Pruritus is often present
7. Signs: Streptococcal Impetigo
   1. Distribution
      1. Affects face, extremities and other exposed areas
   2. Characteristics
      1. Onset with 2 mm Macule or Papule
      2. Rapidly evolves into vessicle and erythematous margin
      3. Vessicle breaks
      4. Leaves Erosion with honey colored crust
   3. Associated findings
      1. Regional Lymphadenopathy
8. Signs: Staphylococcal Impetigo
   1. Similar to Streptococcal Impetigo
   2. Minimal surrounding erythema
   3. Lesion more shallow
9. Complications
   1. Poststreptococcal Glomerulonephritis (1-5% of Impetigo)
      1. Occurs with Streptococcal Impetigo (S. pyogenes)
      2. Not prevented by antibiotic use
10. Labs: Optional (Impetigo is clinical diagnosis)
    1. Lesion Gram Stain reveals Gram Positive Cocci
    2. Lesion culture indications
       1. Poststreptoccal Glomerulonephritis outbreaks
       2. Methicillin-Resistant Staphylococcal aureus suspected
11. Differential Diagnosis
    1. Common
       1. Herpes Simplex Virus (HSV)
       2. Atopic Dermatitis
       3. Contact Dermatitis
       4. Insect Bites
       5. Varicella
       6. Scabies
       7. Inflammatory Superficial Fungal Infection
          1. Candidiasis
          2. Dermatophytosis
    2. Uncommon
       1. Acute pustular Psoriasis
       2. Acute Palmoplantar pustulosis
       3. Primary cutaneous listeriosis (farmers)
       4. Sweet's Syndrome
       5. Pemphigous foliaceus
       6. Ecthyma
       7. Discoid Lupus Erythematosus
12. Course
    1. Mild to moderate cases are non-scarring, self limited
    2. Untreated cases heal in 3-6 weeks
13. Management
    1. Topical therapy (as effective as systemic)
       1. Mupirocin (Bactroban) 2% ointment
          1. Applied three times daily to affected area for 10-12 days
       2. Retapamulin (Altabax) 1% ointment
          1. Apply twice daily to affected area for 5 days
       3. Fusidic Acid 2% cream (Not available in United States)
          1. Apply three times daily to affected area for 10-12 days
          2. Koning (2002) BMJ 324:203-6
    2. Systemic Agents
       1. General
          1. In most cases, topical agents are preferred
          2. Systemics indicated in severe or extensive cases
       2. Preferred systemic agents
          1. Cephalexin (Keflex)
             1. Child: 25-50 mg/kg/day divided bid-qid x10 days
             2. Adult: 250-500 mg PO qid for 10 days
          2. Dicloxacillin
             1. Child: 12.5 to 25 mg/kg/day PO divided qid
             2. Adult: 250-500 mg PO qid for 5-7 days
       3. Other systemic agents with higher resistance rates
          1. Penicillin VK
             1. Child: 25 to 50 mg/kg/day divided qid for 10 days
             2. Adult: 250 mg PO qid for 10 days
          2. Amoxicillin
             1. Child: 40 mg/kg/day PO divided tid for 10 days
             2. Adult: 250 mg PO tid for 10 days
          3. Erythromycin
             1. Child: 30-50 mg/kg/day PO divided qid for 10 days
             2. Adult: 250 mg PO qid for 10 days
    3. Avoid topical disinfectants (no better than Placebo)
       1. Hexachlorophene (Phisohex)
       2. Povidone-Iodine Shampoo offers no benefit
          1. Koning (2002) BMJ 324:203-6
14. References
    1. Cydulka in Marx (2002) Rosen's Emergency Med., p. 1639
    2. Swartz in Mandell (2000) Infectious Disease, p. 1037
    3. Cole (2007) Am Fam Physician 75(6):859-68
    4. Brown (2003) Int J Dermatol 42:251-5