II. 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
- Spreads across body with scratching, towels or clothing resulting in satellite lesions (autoinoculation)
- Spreads easily in daycares and schools
III. 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
IV. Causes
-
Staphylococcus Aureus
- Most common cause of Impetigo
-
Group A Streptococcus (Streptococcus Pyogenes)
- May also cause Impetigo, especially in warm, humid climates
V. 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
VI. Types
-
Bullous Impetigo (less common)
- Staphylococcal toxin mediated reaction
- NonBullous Impetigo (>70%): Described below
- Host response to infection
- Primary Impetigo (most common)
- Due to direct spread of infection
- Secondary Impetigo (Common Impetigo)
- Related to underlying secondary Impetigo cause
- Common predisposing factors (see above)
VII. Symptoms
- Pruritus is often present
VIII. Signs: Streptococcal Impetigo
- Distribution
- Affects face (esp. nares, perioral), extremities and other exposed areas
- Characteristics
- Onset with 2 mm Macule or Papule
- Rapidly evolves into vessicle and erythematous margin
- Vessicle breaks
- Leaves erosion with honey colored crust
- Full skin thickness lesions occur with Ecthyma due to Group A Beta Hemolytic Streptococcus
- Associated findings
IX. Signs: Staphylococcal Impetigo
- Similar to Streptococcal Impetigo
- Minimal surrounding erythema
- Lesion more shallow
X. Complications
- Cellulitis
-
Poststreptococcal Glomerulonephritis (PSGN)
- Occurs with Streptococcal Impetigo caused by S. pyogenes (the Impetigo strains have minimal nephritogenic potential)
- Rare now due to Staphylococcus Aureus as the most Common Impetigo cause (previously 1-5% of Impetigo)
- PSGN is most commonly associated with Streptococcal Pharyngitis (also due to Streptococcus Pyogenes)
- Not prevented by Antibiotic use
XI. Labs: Optional (Impetigo is clinical diagnosis)
- Lesion Gram Stain reveals Gram Positive Cocci
- Lesion culture indications
- Poststreptoccal Glomerulonephritis outbreaks
- Methicillin-Resistant Staphylococcal aureus suspected
XII. Differential Diagnosis
- Common
- Uncommon
- Acute Pustular Psoriasis
- Acute Palmoplantar Pustulosis
- Primary cutaneous Listeriosis (farmers)
- Sweet's Syndrome
- Pemphigous foliaceus
- Ecthyma
- Discoid Lupus Erythematosus (especially childhood)
- Zinc Deficiency (perioral facial rash)
XIII. Course
- Mild to moderate cases are non-scarring, self limited
- Untreated cases heal in 3-6 weeks
- Treated cases resolve more quickly
XIV. Management
- Infections are self-limited even without Antibiotics
- However Antibiotics speed resolution and help to prevent spread to others
- Topical therapy (as effective as systemic)
- Mupirocin (Bactroban) 2% ointment
- Applied three times daily to affected area for 7-10 days
- May be used in age 2 months and older
- Retapamulin (Altabax) 1% ointment
- Apply twice daily to affected area for 5 days
- May be used in age 9 months and older
- Treatment area must be <100 cm2 (or <2% total BSA in children)
- Fusidic Acid 2% cream (Not available in United States)
- Apply three times daily to affected area for 10-12 days
- Koning (2002) BMJ 324:203-6 [PubMed]
- Mupirocin (Bactroban) 2% ointment
- Systemic Agents
- General
- In most cases, topical agents are preferred
- Systemics indicated in severe or extensive cases
- Preferred systemic agents
- Cephalexin (Keflex)
- Child: 25-50 mg/kg/day divided bid-qid x10 days
- Adult: 250-500 mg PO qid for 10 days
- Dicloxacillin
- Child: 12.5 to 25 mg/kg/day PO divided qid
- Adult: 250-500 mg PO qid for 5-7 days
- Cephalexin (Keflex)
- Staphylococcus suspected (especially if suspected MRSA)
- Precautions
- Review local antibiograms to determine local resistance rates
- Given the self-limited nature of Impetigo, consider topical agents only (see above)
- Clindamycin
- Adult: 300-600 every 6-8 hours for 10 days
- Child: 10-25 mg/kg/day divided every 6 to 8 hours
- Doxycycline
- Adult: 100 mg twice daily for 10 days
- Child: Do not use under age 8 years old
- Trimethoprim-Sulfamethoxazole (Septra)
- Adult: 1 tab twice daily for 10 days
- Child: 8-10 mg/kg/day (of trimethoprim component) divided twice daily for 10 days
- Precautions
- Other systemic agents with higher resistance rates
- Precautions
- These agents are not recommended for Impetigo due to high resistance rates
- Also, these are less effective given a predominance of Staphylococcus Aureus in Impetigo
- Penicillin VK
- Child: 25 to 50 mg/kg/day divided qid for 10 days
- Adult: 250 mg PO qid for 10 days
- Amoxicillin
- Child: 40 mg/kg/day PO divided tid for 10 days
- Adult: 250 mg PO tid for 10 days
- Erythromycin
- Child: 30-50 mg/kg/day PO divided qid for 10 days
- Adult: 250 mg PO qid for 10 days
- Precautions
- General
- Avoid Topical Disinfectants (no better than Placebo)
- Hexachlorophene (Phisohex)
- Povidone-IodineShampoo offers no benefit
XV. Prevention
- Clean minor injuries with soap and water
- Regular Handwashing and bathing
- Avoid contact with infected children
XVI. 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]