Workup for Bullous Impetigo
Bullous impetigo is primarily a clinical diagnosis that typically does not require extensive laboratory workup in straightforward cases, but bacterial culture should be obtained when treatment fails, MRSA is suspected, or infections recur. 1, 2
Clinical Diagnosis
The diagnosis of bullous impetigo is made based on characteristic clinical features:
- Fragile, thin-roofed vesicopustules and flaccid bullae that rupture easily, caused exclusively by toxin-producing strains of Staphylococcus aureus 1, 3
- Lesions typically occur on exposed areas (face, extremities) or intertriginous areas 2, 3
- The bullae form when staphylococcal exfoliative toxins cleave the dermal-epidermal junction 1, 4
- More common in children under 5 years of age, particularly neonates 4, 5
When to Obtain Cultures
Bacterial cultures are not routinely necessary for typical presentations, but should be obtained in specific circumstances:
- Treatment failure after 48-72 hours of appropriate therapy 1, 2
- Suspected MRSA infection based on local resistance patterns or clinical context 1, 2
- Recurrent infections requiring identification of the causative organism and antibiotic sensitivities 1, 4
- Outbreaks in institutional settings (wards, nurseries) 4
Culture Technique
- Obtain cultures from vesicle fluid, pus, or erosions 1
- Swab the skin for bacteriological confirmation and antibiotic sensitivities 4
- Consider nasal swabs from the patient and immediate family members to identify asymptomatic carriers of S. aureus 4
What NOT to Do
Do not perform skin biopsies or immunofluorescence studies for typical bullous impetigo—these are reserved for autoimmune blistering disorders like bullous pemphigoid when the diagnosis is uncertain 6, 7
Key Differentiating Features from Bullous Pemphigoid
If the clinical presentation is atypical or not responding to appropriate antibiotics, consider alternative diagnoses:
- Bullous pemphigoid typically affects elderly patients (>70 years), not young children 6
- Bullous pemphigoid presents with tense blisters on erythematous or normal skin, not fragile thin-roofed bullae 6
- Bullous pemphigoid requires skin biopsy with direct immunofluorescence showing linear IgG/C3 deposits at the basement membrane zone 6
Practical Approach
For typical bullous impetigo in children:
- Make the diagnosis clinically based on characteristic fragile bullae 1, 3
- Start empiric topical or oral antibiotics immediately without waiting for cultures 1, 2
- Reserve cultures for treatment failures or suspected MRSA 1, 2
Re-evaluate if no improvement after 48-72 hours and consider obtaining cultures at that point if not already done 1, 2