Impetigo

Introduction | Aetiology and Risk Factors | Pathophysiology | Clinical Presentation | Diagnosis | Differential Diagnosis | Management and Treatment | When to Refer | References

Introduction

Impetigo is a highly contagious superficial bacterial skin infection that commonly affects infants and young children, but it can occur at any age. It typically presents as red sores on the face, particularly around the nose and mouth, and on the hands and feet. The sores burst, develop honey-coloured crusts, and can spread to other parts of the body or to other individuals through direct contact or sharing of items such as towels or toys.

Aetiology and Risk Factors

Impetigo is caused by bacteria, most commonly Staphylococcus aureus and, less frequently, Streptococcus pyogenes (Group A Streptococcus):

• Types of Impetigo:
  • Non-Bullous Impetigo: The most common form, characterised by small vesicles that rupture and form honey-coloured crusts.
  • Bullous Impetigo: Less common, caused by strains of Staphylococcus aureus that produce exfoliative toxins. It presents with larger blisters that can rupture, leaving raw skin underneath.
• Risk Factors:
  • Age: Most common in children, particularly those aged 2 to 5 years.
  • Close Contact: Living in crowded conditions or close contact with an infected person increases the risk of transmission.
  • Skin Trauma: Minor skin injuries, such as cuts, insect bites, or dermatitis, can predispose to impetigo.
  • Poor Hygiene: Lack of regular handwashing or cleaning of skin can contribute to the spread of infection.
  • Warm, Humid Climate: Impetigo is more common in warm, humid environments.
  • Immunosuppression: Individuals with weakened immune systems are at higher risk.
  • Chronic Skin Conditions: Conditions like eczema or scabies can increase susceptibility.

Pathophysiology

Impetigo occurs when bacteria enter the skin through minor breaches in the epidermis:

• Bacterial Colonisation: S. aureus and S. pyogenes can colonise the skin and nasal passages without causing symptoms.
• Skin Barrier Disruption: Cuts, abrasions, or inflammatory skin conditions disrupt the protective barrier, allowing bacteria to invade.
• Toxin Production: In bullous impetigo, exfoliative toxins produced by S. aureus cause cleavage within the epidermis, leading to blister formation.
• Immune Response: The body’s immune response leads to inflammation, resulting in the characteristic signs of redness, swelling, and crusting.

Clinical Presentation

Impetigo presents with the following signs and symptoms, varying slightly between the non-bullous and bullous forms:

• Non-Bullous Impetigo:
  • Begins as small red spots or papules, typically on the face, especially around the nose and mouth.
  • The spots quickly develop into vesicles or pustules that rupture, leaving honey-coloured crusts.
  • Lesions can spread to other parts of the body through scratching or direct contact.
  • Itching is common, but pain is usually minimal.
  • Regional lymphadenopathy may be present.
• Bullous Impetigo:
  • Presents with larger blisters (bullae) filled with yellow or clear fluid, primarily on the trunk, arms, or legs.
  • The bullae eventually rupture, leaving red, raw skin underneath, which may develop a brown crust.
  • More common in neonates and young children but can occur in adults.
  • Systemic symptoms such as fever, weakness, or diarrhoea may occur.
• Ecthyma:
  • A deeper form of impetigo that penetrates into the dermis.
  • Presents with painful ulcers covered with a grey-yellow crust, often on the legs.
  • Heals slowly and may leave scars.

Diagnosis

The diagnosis of impetigo is primarily clinical, based on the characteristic appearance of the lesions:

• Clinical Examination: The presence of honey-coloured crusts on erythematous bases is typically diagnostic of non-bullous impetigo.
• Bacterial Swab: A swab of the affected area may be taken for culture and sensitivity testing, particularly in recurrent cases, severe infections, or when MRSA is suspected.
• Differential Diagnosis: Consider other conditions that may present similarly, such as:
  • Herpes Simplex Virus (HSV): Typically presents with grouped vesicles on erythematous bases.
  • Varicella (Chickenpox): Presents with vesicles in various stages of healing, often widespread.
  • Contact Dermatitis: Erythematous, itchy rash caused by skin contact with allergens or irritants.
  • Scabies: Intense itching with burrows, often in web spaces of fingers.

Differential Diagnosis

It is important to distinguish impetigo from other skin conditions:

• Atopic Dermatitis (Eczema): Chronic, itchy, inflammatory skin condition with a predilection for flexural areas.
• Erysipelas: Acute infection of the upper dermis presenting with a well-demarcated, red, swollen area, often with systemic symptoms.
• Cellulitis: Infection of deeper dermis and subcutaneous tissue, presenting with diffuse redness, warmth, and swelling.
• Insect Bites: Localised erythema and swelling, often with a central punctum.

Management and Treatment

Management of impetigo focuses on eliminating the infection, preventing its spread, and alleviating symptoms:

1. Topical Antibiotics

• Fusidic Acid 2% Cream: Applied three times daily for 7 days to the affected area. Effective for mild to moderate cases of non-bullous impetigo.
• Mupirocin 2% Ointment: Useful for localized infections, especially when fusidic acid resistance is suspected or confirmed.
• Retapamulin 1% Ointment: An alternative topical antibiotic for patients over 9 months old.

2. Oral Antibiotics

• Flucloxacillin: First-line oral antibiotic for extensive or bullous impetigo. Dosage depends on age and severity. Typically prescribed for 7 days.
• Erythromycin or Clarithromycin: Alternatives for patients allergic to penicillin.
• Cephalexin: May be considered in certain cases, bearing in mind cross-reactivity in penicillin-allergic patients.

3. Supportive Care

• Hygiene Measures: Encourage regular handwashing and keeping nails short to prevent the spread of infection. Avoid sharing towels, bedding, or clothing.
• Skin Care: Gently clean the affected area with soap and water before applying topical antibiotics.
• Itch Relief: Oral antihistamines may help alleviate itching, particularly at night.
• Isolation: Keep children with impetigo away from school or nursery until 48 hours after starting antibiotic treatment or until lesions have crusted over.

When to Refer

Referral to a specialist may be necessary in the following situations:

• Severe or Recurrent Cases: If impetigo is severe, recurrent, or does not respond to initial treatment, referral to a dermatologist or paediatrician may be required.
• Suspected Complications: If there are signs of complications such as cellulitis, post-streptococcal glomerulonephritis, or systemic symptoms, referral is recommended.
• Uncertain Diagnosis: If the diagnosis is unclear or if the presentation is atypical, a specialist referral may be necessary for further evaluation and management.
• Immunocompromised Patients: Patients with compromised immune systems may require specialist care.
• Outbreaks: In cases of impetigo outbreaks in schools, nurseries, or care homes, public health involvement may be necessary.

References

1. British Association of Dermatologists (2024) Guidelines for the Management of Impetigo. Available at: https://www.bad.org.uk (Accessed: 26 August 2024).
2. National Institute for Health and Care Excellence (2024) Impetigo: Diagnosis and Management. Available at: https://www.nice.org.uk/guidance/ng153 (Accessed: 26 August 2024).
3. British National Formulary (2024) Topical and Systemic Treatments for Skin Infections. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).