Impetigo
Summary
Impetigo is a highly contagious superficial bacterial skin infection that is extremely common in children, particularly 2-5 years old. It is caused primarily by Staphylococcus aureus (Most common) and/or Streptococcus pyogenes (Group A Strep – GAS). The infection presents as vesicles or pustules that rapidly rupture, leaving characteristic honey-coloured (golden) crusted lesions, typically on the face (Around nose and mouth) and exposed areas. There are two main forms: Non-Bullous Impetigo (Most common – Crusted lesions) and Bullous Impetigo (Flaccid blisters caused by toxin-producing S. aureus). Impetigo is spread by direct contact and is highly contagious; school exclusion is required until lesions have crusted or 48 hours after starting antibiotics. Treatment is topical antibiotics (Fusidic Acid, Mupirocin) for localized disease, or oral antibiotics (Flucloxacillin) for widespread/systemic disease. Rarely, impetigo caused by GAS can lead to Post-Streptococcal Glomerulonephritis. [1,2]
Clinical Pearls
"Honey-Coloured Crusts": The classic appearance – Golden-yellow crusts on an erythematous base. Usually around the mouth and nose.
"Highly Contagious": Spread by direct contact. Outbreaks in schools/nurseries. School exclusion required.
"S. aureus > GAS": Staphylococcus aureus is now the most common cause. GAS still common, especially in developing countries.
"Bullous Impetigo = S. aureus Toxin": Caused by exfoliative toxin-producing S. aureus. Think of it as a localized form of Staphylococcal Scalded Skin Syndrome (SSSS).
Demographics
| Factor | Notes |
|---|---|
| Age | Peak: 2-5 years. Can affect any age. |
| Season | More common in Summer/Autumn. Humid conditions favour transmission. |
| Setting | Schools, Nurseries, Close contacts. Outbreaks common. |
| Prevalence | Very common. One of the most frequent skin infections in children. |
Risk Factors
| Risk Factor | Notes |
|---|---|
| Pre-existing Skin Lesion | Eczema, Insect bites, Cuts, Abrasions. Broken skin allows entry. |
| Poor Hygiene | Close contact, Shared towels/items. |
| Warm/Humid Climate | Tropical/Subtropical regions have higher rates. |
| Crowded Living | Close contact transmission. |
| Nasal Carriage | S. aureus nasal carriage predisposes to self-inoculation. |
Causative Organisms
| Organism | Notes |
|---|---|
| Staphylococcus aureus | Most common cause worldwide. Produces exfoliative toxins (Bullous impetigo). Increasing MRSA strains in some regions. |
| Streptococcus pyogenes (GAS) | Common cause. Associated with rheumatic fever risk (Pharyngeal), PSGN risk (Skin + Pharyngeal). |
| Mixed Infection | Both S. aureus + GAS in same lesion. |
Pathogenesis
- Entry: Bacteria colonise skin (Often from nasal carriage) or enter via break in skin barrier (Eczema, Bite, Cut).
- Superficial Infection: Infection confined to epidermis.
- Vesicle Formation: Inflammatory response → Vesicles/Pustules.
- Rupture: Vesicles rupture → Serous fluid dries to form honey-coloured crusts.
Bullous Impetigo (S. aureus)
- Exfoliative Toxin: Staphylococcal exfoliative toxins A and B target Desmoglein-1 (Same target as in Pemphigus).
- Epidermal Cleavage: Toxin cleaves superficial epidermis → Flaccid blisters.
- Localized SSSS: Bullous impetigo is essentially a localized form of Staphylococcal Scalded Skin Syndrome.
| Type | Features | Causative Organism |
|---|---|---|
| Non-Bullous Impetigo | Vesicles/Pustules → Rupture → Honey-coloured crusts. Around nose/mouth. Most common (~70%). | S. aureus > GAS (Or both). |
| Bullous Impetigo | Flaccid blisters (Bullae) with clear/yellow fluid. Rupture → Thin varnish-like crust. Less common. Occurs on trunk/extremities. | S. aureus (Exfoliative toxin-producing strains). |
| Ecthyma | Deep/ulcerative form. Punched-out ulcers with thick adherent crust. Heals with scarring. | GAS (Or S. aureus). |
Non-Bullous Impetigo
| Feature | Notes |
|---|---|
| Location | Typically perioral (Around mouth) and perinasal (Around nose). Also chin, cheeks. |
| Evolution | Macule → Papule → Vesicle/Pustule (Fragile, ruptures quickly) → Honey-coloured crust on erythematous base. |
| Symptoms | Usually NOT itchy (Unlike eczema). May have mild discomfort. |
| Regional Lymphadenopathy | Common. Tender anterior cervical or submandibular nodes. |
| Systemic Symptoms | Usually absent. Child appears well. |
Bullous Impetigo
| Feature | Notes |
|---|---|
| Location | Trunk, Extremities, Buttocks (Diaper area in infants). Less often face. |
| Lesions | Flaccid blisters (1-5 cm). Clear or cloudy fluid. Rupture easily leaving thin crust or "collarette" of scale. |
| Positive Nikolsky Sign | May be present (Gentle pressure causes epidermis to shear off). |
| Age | More common in infants and young children. |
| Systemic Symptoms | May have low-grade fever. Usually localised – If widespread, consider SSSS. |
Ecthyma
| Feature | Notes |
|---|---|
| Depth | Ulcerative. Involves dermis (Unlike superficial impetigo). |
| Appearance | Punched-out ulcer with thick, adherent, dirty-yellow crust. Erythematous halo. |
| Healing | Slow. Heals with scarring. |
| Risk Factors | Immunocompromise, Poor hygiene, Neglected impetigo. |
Diagnosis
- Clinical Diagnosis: Usually sufficient based on characteristic appearance.
- Swab for Culture: Consider if:
- Treatment failure.
- Recurrent episodes.
- MRSA suspected.
- Immunocompromised patient.
Further Investigations (Rarely Needed)
| Test | Indication |
|---|---|
| Urinalysis | If PSGN suspected (Haematuria, Proteinuria). 1-3 weeks post-streptococcal skin infection. |
| Swab for C&S | Treatment failure, Recurrence, MRSA suspected. |
Management Algorithm
IMPETIGO DIAGNOSED
(Honey-coloured crusts, Vesicles, +/- Bullae)
↓
ASSESS EXTENT
- Localized (Few lesions, Small area)?
- Widespread (Many lesions, Large area)?
- Systemic symptoms (Fever, Unwell)?
↓
LOCALIZED (Most Cases)
┌──────────────────────────────────────────────────────────┐
│ TOPICAL ANTIBIOTIC (First-Line) │
│ │
│ - **Fusidic Acid 2% cream/ointment** TDS for 5-7 days │
│ OR │
│ - **Mupirocin 2% ointment** TDS for 5-7 days │
│ (Preferred if MRSA suspected) │
│ │
│ HYGIENE MEASURES: │
│ - Wash crusts gently with soap and water before │
│ applying antibiotic │
│ - Separate towels/flannels │
│ - Hand washing after touching lesions │
│ - Keep nails short │
└──────────────────────────────────────────────────────────┘
↓
WIDESPREAD / SYSTEMIC / FAILED TOPICAL
┌──────────────────────────────────────────────────────────┐
│ ORAL ANTIBIOTIC │
│ │
│ - **Flucloxacillin** (Anti-staphylococcal) │
│ Child less than 2: 62.5mg QDS for 5-7 days │
│ Child 2-9: 125mg QDS │
│ Child 10-17: 250mg QDS │
│ │
│ PENICILLIN ALLERGY: │
│ - **Clarithromycin** or **Erythromycin** │
│ │
│ MRSA SUSPECTED: │
│ - Swab for C&S. Discuss with micro. │
│ - Doxycycline (>12 years), Trimethoprim, Clindamycin │
└──────────────────────────────────────────────────────────┘
↓
SCHOOL EXCLUSION
- Until lesions crusted over
- OR 48 hours after starting antibiotic treatment
Hygiene Measures (All Patients)
| Measure | Notes |
|---|---|
| Handwashing | Regular, Especially after touching lesions. |
| Separate Towels/Flannels | Do not share. Wash at high temperature. |
| Crust Removal | Gently soak off crusts before applying topical treatment. Improves antibiotic penetration. |
| Keep Nails Short | Reduces scratching and spread. |
| Avoid Touching Lesions | Minimise auto-inoculation. |
| Complication | Notes |
|---|---|
| Cellulitis | Deeper soft tissue infection. Spreading erythema, Fever. Requires oral/IV antibiotics. |
| Lymphangitis | Red streaking along lymphatics. |
| Post-Streptococcal Glomerulonephritis (PSGN) | 1-3 weeks after GAS skin infection. Haematuria, Oedema, Hypertension. NOT prevented by antibiotics. |
| Scarring | Ecthyma heals with scars. Impetigo usually heals without scarring. |
| Staphylococcal Scalded Skin Syndrome (SSSS) | In neonates/young infants with bullous impetigo from toxin-producing S. aureus. Widespread epidermal loss. |
| Factor | Notes |
|---|---|
| Prognosis | Excellent. Resolves with treatment in 7-10 days. |
| Without Treatment | Lesions often resolve spontaneously within 2-3 weeks but can spread. |
| Recurrence | Common, Especially if nasal carriage of S. aureus. May need decolonisation. |
| Scarring | Non-bullous impetigo and bullous impetigo usually heal without scarring. Ecthyma scars. |
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Impetigo | NICE CKS (2023) | Topical for localised. Oral for widespread. Fusidic acid or Mupirocin. |
| Infection Control | PHE | Exclusion from school until 48h after antibiotics or lesions crusted. |
Antibiotic Stewardship
- Topical treatment preferred for localised disease (Reduces systemic antibiotic use).
- Consider MRSA in treatment failure or endemic areas.
What is Impetigo?
Impetigo is a common skin infection in children caused by bacteria. It appears as blisters or sores that burst and leave behind golden-yellow crusts. It usually happens around the mouth and nose but can appear anywhere.
Is it contagious?
Very! It spreads easily through touch and sharing items like towels. Your child should stay home from school until the sores have crusted over or they have been on antibiotics for 48 hours.
What causes it?
Bacteria (Staph or Strep) get into the skin through a scratch, insect bite, or even from eczema. The bacteria cause an infection just under the skin surface.
How is it treated?
- Antibiotic cream (Applied directly to the sores) for mild cases.
- Antibiotic tablets for more widespread infection.
- Good hygiene: Wash hands, Separate towels, Don't share items.
Will it scar?
Ordinary impetigo heals without scarring. A deeper form (Ecthyma) can sometimes leave small scars.
Primary Sources
- National Institute for Health and Care Excellence. Impetigo: Clinical Knowledge Summaries. 2023. cks.nice.org.uk/topics/impetigo
- Koning S, et al. Interventions for impetigo. Cochrane Database Syst Rev. 2012;(1):CD003261. PMID: 22258953.
Common Exam Questions
- Classic Appearance: "Describe the classic appearance of Non-Bullous Impetigo."
- Answer: Honey-coloured (Golden) crusts on an erythematous base, typically perioral/perinasal.
- Causative Organism: "What is the most common causative organism?"
- Answer: Staphylococcus aureus (Can also be GAS or mixed).
- Bullous Impetigo Mechanism: "What causes the blisters in Bullous Impetigo?"
- Answer: Exfoliative toxins from S. aureus (Target Desmoglein-1).
- Treatment (Localised): "What is first-line treatment for localised impetigo?"
- Answer: Topical Fusidic Acid or Topical Mupirocin for 5-7 days.
Viva Points
- Ecthyma vs Impetigo: Ecthyma is deeper (Ulcerative), Heals with scarring.
- PSGN Risk: Post-Streptococcal Glomerulonephritis can follow GAS skin infection. NOT prevented by antibiotics.
- Nasal Decolonisation: For recurrent impetigo – Mupirocin nasal ointment + Chlorhexidine washes.
- SSSS Spectrum: Bullous impetigo is the localised form. SSSS is the generalized form.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.