Impetigo

Definition

Impetigo is a highly contagious superficial bacterial skin infection, most common in children but can affect individuals of any age. It is characterized by pustules and honey-colored crusts and is typically caused by Staphylococcus aureus and/or Streptococcus pyogenes (group A beta-hemolytic streptococcus).

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Types

1. Non-bullous impetigo

   • Most common form

   • Presents with small vesicles or pustules that rupture, leaving erosions covered by yellowish (honey-colored) crusts

   • Often affects the face, especially around the nose and mouth, and the extremities

2. Bullous impetigo

   • Caused by S. aureus producing exfoliative toxins

   • Presents with larger fluid-filled bullae that rupture, leaving a thin brown crust

   • More common in infants and young children

3. Ecthyma

   • A deeper form of impetigo involving the dermis

   • Presents with ulcerative lesions covered by thick crust

   • Heals with scarring

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Risk Factors

• Warm, humid climates

• Poor hygiene or crowded living conditions

• Minor skin trauma (scratches, insect bites)

• Pre-existing skin disease (eczema, scabies)

• Immunocompromised state

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Pathophysiology

Bacteria invade the superficial layers of the skin via minor breaks in the epidermis.

• S. aureus: Commonly colonizes the skin and nasal passages; produces toxins causing blistering in bullous form

• S. pyogenes: Can cause non-bullous impetigo; risk of post-streptococcal glomerulonephritis

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Clinical Features

Non-bullous impetigo

• Initial small red macules or papules → vesicles/pustules

• Rapid rupture leaving erosions with adherent honey-colored crusts

• Mild pruritus; usually not painful

Bullous impetigo

• Large, flaccid bullae with clear or yellow fluid

• Minimal surrounding erythema

• Rupture leaves thin brown crusts

Ecthyma

• Punched-out ulcers with thick adherent crust

• More indurated and painful; potential scarring

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Diagnosis

• Usually clinical based on characteristic appearance

• Bacterial swab and culture for recurrent, widespread, or MRSA-suspected cases

• Consider sensitivity testing if empirical therapy fails

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Management

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General Measures

• Maintain good hygiene; wash lesions gently with soap and water

• Keep fingernails short to reduce spread from scratching

• Avoid sharing towels, bedding, or clothing

• Children should stay out of school/nursery until 24 hours after starting antibiotic treatment or until lesions are dry/crusted over

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Pharmacological Treatment

1. Topical antibiotics (for localized non-bullous impetigo)

• Fusidic acid 2% cream/ointment: Apply thinly to affected area 3–4 times daily for 5–7 days

• Mupirocin 2% ointment: Apply thinly 3 times daily for 5–7 days (especially if MRSA suspected)

• Retapamulin 1% ointment: Apply twice daily for 5 days (alternative in some countries)

2. Oral antibiotics (for extensive disease, bullous impetigo, systemic symptoms, or failure of topical therapy)

First-line (non-penicillin allergic):

• Flucloxacillin: Adults 500 mg orally every 6 hours for 7 days; Children 12.5–25 mg/kg every 6 hours (max 1 g/dose)

Alternative for penicillin allergy:

• Clarithromycin: Adults 250–500 mg orally every 12 hours for 7 days; Children 7.5 mg/kg orally every 12 hours (max 500 mg/dose)

• Erythromycin: 250–500 mg orally every 6 hours for 7 days

If MRSA suspected/confirmed:

• Doxycycline: 100 mg orally once daily for 7 days (adults; not for children <8 years)

• Trimethoprim-sulfamethoxazole: Dose according to trimethoprim component (adults 160 mg twice daily for 7 days)

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Complications

• Local spread causing cellulitis

• Lymphangitis

• Post-streptococcal glomerulonephritis (rare but possible after S. pyogenes infection)

• MRSA-related infections in resistant cases

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Prevention

• Prompt cleaning of minor cuts, scrapes, and insect bites

• Good personal hygiene

• Early treatment of skin infections to limit spread

• Screening and decolonization in recurrent or outbreak cases (e.g., intranasal mupirocin for nasal carriage of S. aureus)