Impetigo

See Also

Bullous Impetigo

Epidemiology

Preschool children (age 2-5 years old) most often affected
Most common Bacterial Skin Infection in children
Non-Bullous Impetigo represents 70% of cases, whereas Bullous Impetigo represents the remainder
Highly contagious
1. Spreads across body with scratching, towels or clothing resulting in satellite lesions (autoinoculation)
2. Spreads easily in daycares and schools

Pathophysiology

Streptococcus Pyogenes and Staphylococcus aureus normally colonize the nose and pharynx, axilla and perineum
Local Skin Trauma allows colonizing Bacteria to break through skin barrier and results in localized infection

Causes

Staphylococcus aureus
1. Most common cause of Impetigo
Group A Streptococcus (Streptococcus Pyogenes)
1. May also cause Impetigo, especially in warm, humid climates

Predisposing factors

Minor Skin Trauma (e.g. abrasions, Insect Bites)
Hot, humid weather
Poor hygiene
Daycare attendence
Over-crowded living conditions
Comorbid conditions (especially Diabetes Mellitus)
Malnutrition
Atopic Dermatitis
Dialysis

Types

Bullous Impetigo (less common)
1. Staphylococcal toxin mediated reaction
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

Pruritus is often present

Signs
Streptococcal Impetigo

Distribution
1. Affects face (esp. nares, perioral), extremities and other exposed areas
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
Associated findings
1. Regional Lymphadenopathy

Signs
Staphylococcal Impetigo

Similar to Streptococcal Impetigo
Minimal surrounding erythema
Lesion more shallow

Complications

Cellulitis
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)

Lesion Gram Stain reveals Gram Positive Cocci
Lesion culture indications
1. Poststreptoccal Glomerulonephritis outbreaks
2. Methicillin-Resistant Staphylococcal aureus suspected

Differential Diagnosis

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)
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)
8. Zinc Deficiency (perioral facial rash)

Course

Mild to moderate cases are non-scarring, self limited
1. Untreated cases heal in 3-6 weeks
2. Treated cases resolve more quickly

Management

Infections are self-limited even without antibiotics
1. However antibiotics speed resolution and help to prevent spread to others
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]
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
Avoid Topical Disinfectants (no better than Placebo)
1. Hexachlorophene (Phisohex)
2. Povidone-IodineShampoo offers no benefit
  1. Koning (2002) BMJ 324:203-6 [PubMed]

Prevention

Clean minor injuries with soap and water
Regular Handwashing and bathing
Avoid contact with infected children

References

Cydulka in Marx (2002) Rosen's Emergency Med., p. 1639
Swartz in Mandell (2000) Infectious Disease, p. 1037
Cole (2007) Am Fam Physician 75(6):859-68 [PubMed]
Brown (2003) Int J Dermatol 42:251-5 [PubMed]
Hartman-Adams (2014) 90(4): 229-35 [PubMed]