Impetigo

Epidemiology

• Affects a median of 45% of Indigenous children at any one time
• Most common in preschool children (ages 2-5)
• Most common bacterial skin infection in children
• Non-Bullous Impetigo: 70% of cases
• Bullous Impetigo: Remaining cases
• Highly contagious, spreads via scratching, towels, or clothing
• Common in daycares and schools

Pathophysiology

• Colonization Sites: Nose, pharynx, axilla, perineum
• Bacteria: Streptococcus pyogenes and Staphylococcus aureus
• Local skin trauma allows bacteria to breach the skin barrier, leading to localized infection

Causes

• Staphylococcus aureus: Most common cause
• Group A Streptococcus (Streptococcus pyogenes): Also causes impetigo, especially in warm, humid climates

Predisposing Factors

• Minor skin trauma (e.g., abrasions, insect bites)
• Hot, humid weather
• Poor hygiene
• Daycare attendance
• Overcrowded living conditions
• Comorbid conditions (e.g., diabetes mellitus)
• Malnutrition
• Atopic dermatitis
• Dialysis

Types of Impetigo

Bullous Impetigo

• Less common
• Staphylococcal toxin-mediated reaction

Non-Bullous Impetigo

• More than 70% of cases
• Host response to infection

Primary Impetigo

• Due to direct spread of infection

Secondary Impetigo

• Predisposing Factors:
  • Diabetes mellitus
  • AIDS
  • Herpes simplex virus
  • Varicella
  • Insect bites

Symptoms

• Pruritus (itching) is often present

Signs

Streptococcal Impetigo

• Distribution: Face (especially nares, perioral), extremities, and other exposed areas
• Characteristics:
  • Begins with 2 mm macule or papule
  • Evolves into vesicle with erythematous margin
  • Vesicle breaks, leaves erosion with honey-colored crust
  • Regional lymphadenopathy

Staphylococcal Impetigo

• Similar to streptococcal impetigo
• Minimal surrounding erythema
• More shallow lesions

Complications

• Cellulitis
• Poststreptococcal Glomerulonephritis (PSGN):
  • Occurs with streptococcal impetigo caused by S. pyogenes
  • Rare due to Staphylococcus aureus being the most common cause now
  • Most commonly associated with streptococcal pharyngitis
  • Not prevented by antibiotic use

Differential Diagnosis

Common

• Herpes simplex virus (HSV)
• Atopic dermatitis
• Contact dermatitis
• Insect bites
• Varicella
• Scabies
• Inflammatory superficial fungal infection
• Cutaneous candidiasis
• Dermatophytosis (e.g., tinea capitis)

Uncommon

• Acute pustular psoriasis
• Acute palmoplantar pustulosis
• Primary cutaneous listeriosis (farmers)
• Sweet’s syndrome
• Pemphigus foliaceus
• Ecthyma
• Discoid lupus erythematosus (especially childhood)

Course

• Mild to moderate cases are non-scarring and self-limited
• Untreated cases heal in 3-6 weeks
• Treated cases resolve more quickly

Management

• Infections are self-limited, but antibiotics speed resolution and prevent spread

Topical Therapy

• Mupirocin (Bactroban) 2% ointment:
  • Applied three times daily for 7-10 days
  • Suitable for ages 2 months and older

Systemic Agents

• Indicated in severe or extensive cases

Cephalexin (Keflex)

• Child: 25-50 mg/kg/day divided bid-qid for 10 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

Staphylococcus Suspected (especially MRSA)

• Avoid topical disinfectants (no better than placebo)
• Hexachlorophene (Phisohex) and Povidone-Iodine Shampoo offer no benefit

Prevention

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