Impetigo

See Also

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 households, 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, esp. in resource rich countries and temperate climates
2. Spreads via skin to skin contact and fomites (e.g. towels)
3. Not correlated with nasal carriage of staphyloccus aureus
Group A Streptococcus (Streptococcus Pyogenes)
1. May also cause Impetigo, especially in warm, humid climates (endemic regions)
2. Spreads via skin to skin contact and respiratory secretions
3. Asymptomatic pharyngeal carriers in 3% of adults and 8% of children (up to 50% during school outbreaks)

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
Hemodialysis

Types

Bullous Impetigo (less common)
1. Staphylococcal toxin mediated reaction
2. Affects only the superficial Epidermis
NonBullous Impetigo (>70%): Described below
1. Host response to infection
2. Primary Impetigo (most common)
  1. Due to direct spread of infection (Staphylococcus Aureus and/or Group A Streptococcus)
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 Vesicle and erythematous margin
3. Vesicle breaks
4. Leaves erosion with honey colored crust
5. Full skin thickness lesions occur with Ecthyma due to Group A Beta Hemolytic Streptococcus
Associated findings
1. Regional Lymphadenopathy

Signs
Staphylococcal Impetigo

See Bullous Impetigo (30% of cases)
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
Rheumatic Fever
1. Associated with Group A Streptococcus (typically Pharyngitis)

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

General measures
1. Soap and water to remove crusts
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 5 days
  2. May be used in age 2 months and older
  3. Broad spectrum coverage against Group A Streptococcus, MSSA, MRSA and some Gram Negatives
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)
  4. Bacteriostatic against Group A Streptococcus and MSSA (but not MRSA)
  5. Much more expensive than Mupirocin with less coverage
3. Ozenoxacin (Xepi)
  1. Topical Quinolone with minimal systemic absorption and FDA approved for age >2 months
  2. Released in 2017, but discontinued in U.S. in 2025
  3. Available internationally outside the U.S.
  4. Bacteriocidal against Group A Streptococcus, MSSA, MRSA
4. Fusidic Acid 2% cream (Not available in United States)
  1. Apply three times daily to affected area for 5 days
  2. Koning (2002) BMJ 324:203-6 [PubMed]
Systemic Agents
1. General
  1. In most cases, topical agents are preferred
  2. When systemic Antibiotics are used, limit to narrow spectrum (GAS, MSSA, MRSA) and for 7-10 days
  3. Systemic Antibiotic indications
    1. Severe or extensive cases
    2. Unresponsive to topicals after 3-5 days
    3. Outbreaks affecting multiple patients
2. Preferred systemic agents (for 7-10 days)
  1. Cephalexin (Keflex)
    1. Child: 25-50 mg/kg/day divided three times daily to four times daily
    2. Adult: 250-500 mg orally three to four times daily
  2. Dicloxacillin
    1. Child: 12.5 to 25 mg/kg/day orally divided three times daily to four times daily
    2. Adult: 250-500 mg orally three to four times daily
3. Staphylococcus suspected (especially if suspected MRSA, for 7-10 days)
  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
    2. Child: 10-25 mg/kg/day divided every 6 to 8 hours
  3. Doxycycline
    1. Adult (or wt >45 kg): 100 mg orally twice daily
    2. Child (wt <45 kg): 2 mg/kg up to 100 mg orally twice daily
      1. Avoid use under age 8 years old
  4. Trimethoprim-Sulfamethoxazole (Septra DS, Bactrim DS)
    1. Adult: 1 tab orally twice daily
    2. Child: 8-10 mg/kg/day (of trimethoprim component) orally divided twice daily
AVOID Topical Disinfectants (no better than Placebo or soap and water, and may cause irritation)
1. Chlorhexidine
2. Hexachlorophene (Phisohex)
3. 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, including cleaning under Fingernails
Thoroughly wash clothing, towels, bedding and toys with detergents and antiseptics after Impetigo exposure
Avoid contact with infected patients (esp. children)
1. May Return to School, daycare 12-24 hours after starting Antibiotics (or after clinical improvement begins)
2. Cover active lesions if possible

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]
Trang (2026) Am Fam Physician 113(2): 175-80 [PubMed]