Bacteria

Impetigo

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Impetigo, NonBullous Impetigo, Streptococcal Impetigo, Staphylococcal Impetigo, Common Impetigo

  • See Also
  • Epidemiology
  1. Preschool children (age 2-5 years old) most often affected
  2. Most common Bacterial Skin Infection in children
  3. Non-Bullous Impetigo represents 70% of cases, whereas Bullous Impetigo represents the remainder
  4. Highly contagious
    1. Spreads across body with scratching, towels or clothing resulting in satellite lesions (autoinoculation)
    2. Spreads easily in daycares and schools
  • Pathophysiology
  1. Streptococcus Pyogenes and Staphylococcus aureus normally colonize the nose and pharynx, axilla and perineum
  2. Local Skin Trauma allows colonizing Bacteria to break through skin barrier and results in localized infection
  • Causes
  1. Staphylococcus aureus
    1. Most common cause of Impetigo
  2. Group A Streptococcus (Streptococcus Pyogenes)
    1. May also cause Impetigo, especially in warm, humid climates
  • Predisposing factors
  1. Minor Skin Trauma (e.g. abrasions, Insect Bites)
  2. Hot, humid weather
  3. Poor hygiene
  4. Daycare attendence
  5. Over-crowded living conditions
  6. Comorbid conditions (especially Diabetes Mellitus)
  7. Malnutrition
  8. Atopic Dermatitis
  9. Dialysis
  • 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
      2. Common predisposing factors (see above)
        1. Diabetes Mellitus
        2. AIDS
        3. Herpes Simplex Virus
        4. Varicella
        5. Insect Bites
  • Symptoms
  1. Pruritus is often present
  • Signs
  • Streptococcal Impetigo
  1. Distribution
    1. Affects face (esp. nares, perioral), 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
  • Signs
  • Staphylococcal Impetigo
  1. Similar to Streptococcal Impetigo
  2. Minimal surrounding erythema
  3. Lesion more shallow
  • Complications
  1. Cellulitis
  2. Poststreptococcal Glomerulonephritis (PSGN)
    1. Occurs with Streptococcal Impetigo caused by S. pyogenes (the Impetigo strains have minimal nephritogenic potential)
    2. Rare now due to Staphylococcus aureus as the most Common Impetigo cause (previously 1-5% of Impetigo)
    3. PSGN is most commonly associated with Streptococcal Pharyngitis (also due to Streptococcus Pyogenes)
    4. Not prevented by antibiotic use
  • 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
  • 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. Cutaneous Candidiasis
      2. Dermatophytosis (e.g. Tinea Capitis)
  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 (especially childhood)
  • Course
  1. Mild to moderate cases are non-scarring, self limited
    1. Untreated cases heal in 3-6 weeks
    2. Treated cases resolve more quickly
  • Management
  1. Infections are self-limited even without antibiotics
    1. However antibiotics speed resolution and help to prevent spread to others
  2. Topical therapy (as effective as systemic)
    1. Mupirocin (Bactroban) 2% ointment
      1. Applied three times daily to affected area for 7-10 days
      2. May be used in age 2 months and older
    2. Retapamulin (Altabax) 1% ointment
      1. Apply twice daily to affected area for 5 days
      2. May be used in age 9 months and older
      3. Treatment area must be <100 cm2 (or <2% total BSA in children)
    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 [PubMed]
  3. 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. Staphylococcus suspected (especially if suspected MRSA)
      1. Precautions
        1. Review local antibiograms to determine local resistance rates
        2. Given the self-limited nature of Impetigo, consider topical agents only (see above)
      2. Clindamycin
        1. Adult: 300-600 every 6-8 hours for 10 days
        2. Child: 10-25 mg/kg/day divided every 6 to 8 hours
      3. Doxycycline
        1. Adult: 100 mg twice daily for 10 days
        2. Child: Do not use under age 8 years old
      4. Trimethoprim-Sulfamethoxazole (Septra)
        1. Adult: 1 tab twice daily for 10 days
        2. Child: 8-10 mg/kg/day (of trimethoprim component) divided twice daily for 10 days
    4. Other systemic agents with higher resistance rates
      1. Precautions
        1. These agents are not recommended for Impetigo due to high resistance rates
        2. Also, these are less effective given a predominance of Staphylococcus aureus in Impetigo
      2. Penicillin VK
        1. Child: 25 to 50 mg/kg/day divided qid for 10 days
        2. Adult: 250 mg PO qid for 10 days
      3. Amoxicillin
        1. Child: 40 mg/kg/day PO divided tid for 10 days
        2. Adult: 250 mg PO tid for 10 days
      4. Erythromycin
        1. Child: 30-50 mg/kg/day PO divided qid for 10 days
        2. Adult: 250 mg PO qid for 10 days
  4. Avoid topical disinfectants (no better than Placebo)
    1. Hexachlorophene (Phisohex)
    2. Povidone-Iodine Shampoo offers no benefit
      1. Koning (2002) BMJ 324:203-6 [PubMed]
  • Prevention
  1. Clean minor injuries with soap and water
  2. Regular Handwashing and bathing
  3. Avoid contact with infected children
  • 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 [PubMed]
  4. Brown (2003) Int J Dermatol 42:251-5 [PubMed]
  5. Hartman-Adams (2014) 90(4): 229-35 [PubMed]