Impetigo
Impetigo is a common, highly contagious superficial bacterial skin infection, most often affecting young children.
This updated UKMLA guide to impetigo is based on NICE NG153 and NICE CKS, which covers causes, risk factors, symptoms, bullous vs non-bullous impetigo, diagnosis, and management.
Epidemiology
Impetigo can affect any age, but is most common in young children
- Mainly 2-5 y/o for non-bullous impetigo
- <2 y/o for bullous impetigo
Causes and Risk Factors
Impetigo is caused by a bacterial infection
- Most common: Staphylococcus aureus
- Rarely: Streptococcus pyogenes (GAS)
Bullous impetigo is almost always caused by Staphylococcus aureus. Exfoliative toxins produced by the bacteria target desmoglein-1 (an intracellular adhesion molecule), leading to loss of cell adhesion and subsequent bullae formation.
Risk factors:
- Causes of skin break (e.g. cuts, burns, bites, eczema, contact dermatitis)
- Warm / humid weather
- Poor hygiene
- Crowded and impoverished environments
- Immunosuppression (e.g. diabetes, malnutrition)
Impetigo is highly contagious, most commonly spread through direct contact with an infected person. Autoinoculation via fingers or contaminated objects (e.g. toys, towels, clothing) can lead to satellite lesions in adjacent areas.
Clinical Features
| Feature | Non-bullous impetigo (70%) | Bullous impetigo (30%) |
|---|---|---|
| Location |
Mucosal involvement is uncommon |
Buccal mucosa may be involved |
| Appearance and progression | Maculopapular lesion → vesicles / pustules (often transient and not always seen clinically) → rupture → exudate dries to form the classic golden-brown / honey-coloured crusts
Usually asymptomatic, with occasional pruritus Satellite lesions may develop following autoinoculation |
Small vesicles → flaccid bullae (>1 cm fluid-filled lesions) → rupture → collarette of scale / crust formation
Systemic upset (e.g. fever, lymphadenopathy, weakness) may be present if large areas of skin are affected Bullous impetigo has a -ve Nikolsky sign, which helps differentiate it from other blistering skin conditions (e.g. SJS) |
Investigation and Diagnosis
Impetigo is primarily a clinical diagnosis, investigations are not routinely needed.
Only consider swabs (of exudate / pus) for culture and sensitivities if:
- Failed to respond to treatment
- Recurrent / widespread impetigo
- Diagnostic uncertainty
- MRSA suspected
Management
Conservative / General Management
Advice on:
- Impetigo is usually self-limiting (heals in 7-21 days without treatment)
- Hygiene measures
- Exclusion from childcare facilities / school / work is recommended:
- Until all lesions are crusted and healed, or
- Until 48 hours after starting antibiotic treatment
Pharmacological Management
Choice of route and drug depends on the type and extent of impetigo.
Notes on suspected / confirmed MRSA infection
- It is advised to seek further microbiology specialist input to determine antibiotic choice
- Of the available topical antibiotics, topical mupirocin is active against MRSA
Non-bullous Impetigo
Choice depends on the extent of impetigo:
| Extent of impetigo | Management |
|---|---|
| Localised disease | 1st line: topical hydrogen peroxide 1%
Alternative: topical antibiotics (1st line: fusidic acid 2%; 2nd line: mupirocin 2%) |
| Widespread disease | Offer antibiotics for 5 days
Choice of route:
Choice of antibiotics:
|
Topical hydrogen peroxide should NOT be used if impetigo is around the eyes.
Use topical antibiotics instead.
If the 1st line measures are not effective / inappropriate, step up according to this ladder:
- Topical hydrogen peroxide
- Topical antibiotics
- Oral antibiotics
This means that if hydrogen peroxide did not work → step up to topical antibiotics. If topical antibiotics did not work → step up to oral antibiotics
Bullous Impetigo / Systemically Unwell
Offer oral antibiotics for 5 days:
- 1st line: flucloxacillin
- 2nd line (e.g. penicillin allergy): clarithromycin / erythromycin (in pregnancy)
References