Impetigo
Exam Tips
- Differentiate by morphology: non-bullous impetigo gives honey-coloured crusts; bullous impetigo gives flaccid bullae then collarette scale after rupture.
- Impetigo is usually a clinical diagnosis; swab only when recurrent, widespread, treatment-refractory, uncertain diagnosis, or MRSA concern.
- In OSCEs, always add infection-control counselling (hand hygiene, no sharing towels, lesion covering, exclusion advice) plus safety-netting for rapid worsening/systemic illness.
- Know urgency triggers for referral: suspected deep soft-tissue infection/sepsis, significant immunosuppression with widespread disease, or diagnostic uncertainty.
Definition
Impetigo is a highly contagious, superficial bacterial infection of the epidermis, most often seen in children in primary care. It presents as either non-bullous disease with rapidly rupturing pustules/vesicles and honey-coloured crusts, or bullous disease with flaccid bullae caused by staphylococcal toxin-mediated epidermal splitting.
Pathophysiology
Most cases are due to Staphylococcus aureus and/or Group A beta-haemolytic Streptococcus (Streptococcus pyogenes), entering via minor skin barrier disruption (primary on intact skin or secondary over eczema, bites, trauma, scabies). In bullous impetigo, S. aureus exfoliative toxins cleave desmoglein-1 in the granular epidermis, causing intraepidermal blistering and fragile bullae. Autoinoculation from fingers, towels, clothing, and close contact explains clustering of lesions and rapid household spread after an incubation of about 4-10 days.
Risk Factors
- Young age (especially 2-5 years for non-bullous; <2 years for bullous)
- Breaks in skin integrity (eczema, dermatitis, insect bites, cuts, burns, scabies)
- Close contact exposure to infected person
- Crowding, poor hygiene, humid/warm environments
- Diabetes, malnutrition, or other immunosuppressive states
- Staphylococcal carriage and prior recurrent impetigo
- Possible MRSA exposure/risk factors
Clinical Features
Symptoms
- Often mild or asymptomatic skin eruption
- Local itch or irritation; pain usually minimal
- Spread of lesions to adjacent sites from scratching/autoinoculation
- Systemic symptoms usually absent in limited disease, but fever/malaise can occur if extensive (more likely in bullous disease)
Signs
- Non-bullous: transient vesicles/pustules that rupture quickly, leaving golden-brown (honey-coloured) crusts with minimal surrounding erythema
- Common distribution: face (around nose/mouth), limbs, and flexures (including axillae)
- Satellite lesions and regional lymphadenopathy may occur in non-bullous disease
- Bullous: large fragile flaccid bullae (>1 cm) that rupture to leave erosions with a collarette of scale and thin brown crust
- Bullous lesions often on flexures, trunk, face, limbs; mucosal involvement can occur
- Clinical image correlation: honey-coloured crusts and post-bullous collarette scale are classic visual exam clues (see representative dermatology atlas/BAD impetigo images)
Investigations
Management
Lifestyle Modifications
- Clean affected skin gently with soap and water; remove crusts carefully where practical
- Avoid touching/scratching lesions; strict hand hygiene after contact
- Cover lesions when possible to reduce transmission
- Do not share towels, clothing, bedding, or personal-care items
- Daily cleaning of frequently touched objects (toys/play equipment)
- Wash clothing/bedding at high temperature (about 60C) and change daily in early treatment phase
- Exclude from school/work/childcare until lesions have healed or until 48 hours after starting effective antibiotic treatment (local policy may vary)
Pharmacological Treatment
Topical antiseptic (first-line for localised non-bullous impetigo)
- Hydrogen peroxide 1% cream: apply 2-3 times daily for 5 days
Appropriate for mild localised disease; avoid in/near eyes and stop if significant local irritation develops.
Topical antibiotic (if topical antiseptic unsuitable or ineffective; localised non-bullous)
- Fusidic acid 2% cream/ointment: apply three times daily for 5 days
Use short courses only to limit antimicrobial resistance; not preferred for extensive disease. Consider microbiology advice if recurrent disease or concern for resistance.
Oral antibiotic (widespread non-bullous, bullous, severe disease, or systemic features)
- Flucloxacillin: 500 mg four times daily for 5 days (adults; paediatric dosing by age/weight per BNF)
- Clarithromycin: 500 mg twice daily for 5 days if penicillin allergy (non-pregnant; paediatric dosing per BNF)
- Erythromycin: 500 mg four times daily for 5 days as preferred macrolide in pregnancy when needed (paediatric dosing per BNF)
Safety: check immediate penicillin hypersensitivity before flucloxacillin; monitor for hepatic adverse effects/cholestatic jaundice with flucloxacillin, especially in prolonged/repeated exposure. Clarithromycin has important CYP3A4 interactions (e. g, statins), and QT-prolongation risk. Seek microbiology input when MRSA is suspected and tailor to culture results.
Complications
- Cellulitis
- Ecthyma (deeper dermal extension)
- Staphylococcal scalded skin syndrome
- Lymphangitis
- Osteomyelitis or septic arthritis (rare)
- Bacteraemia/sepsis
- Post-streptococcal sequelae: acute glomerulonephritis (typically 1-2 weeks later), scarlet fever-related phenomena
- Scarring (uncommon)
Prognosis
Overall prognosis is good: untreated lesions often resolve in about 7-21 days, and most patients heal without scarring. Appropriate treatment shortens infectivity and may speed recovery, while recurrence is more likely with persistent risk factors (for example eczema, staphylococcal carriage, or crowded living conditions).
Sources & References
🏥BMJ Best Practice(1)
💊BNF Drug References(2)
- Clarithromycin[management.pharmacological]
- Flucloxacillin[management.pharmacological]
✅NICE Guidelines(1)
- Impetigo[overview]
📖Textbook References(2)
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 164, 165)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 599)[context]