How to diagnose staph bullous impetigo?

Diagnosis of Staph Bullous Impetigo

The diagnosis of staph bullous impetigo should be based primarily on its characteristic clinical presentation of large, flaccid bullae that rupture easily, leaving a thin collarette of scale at the periphery of denuded areas, typically affecting intertriginous areas. 1

Clinical Presentation

• Characteristic appearance:

  • Large, flaccid bullae (fluid-filled blisters)
  • Honey-colored crusts after bullae rupture
  • Thin collarette of scale at periphery of denuded areas
  • More likely to affect intertriginous areas 1, 2
  • May present with erythema, tenderness, and induration 1

• Distribution patterns:

  • Most common in children 2-5 years of age
  • Can affect neonates and infants (higher risk group)
  • Often appears on face, extremities, and intertriginous areas 2

Diagnostic Approach

1. Visual examination:

   • Identify characteristic bullae and honey-colored crusts
   • Differentiate from non-bullous impetigo (which presents with smaller pustules and crusted lesions)

2. Microbiological confirmation:

   • Gram stain and culture of pus or exudates from skin lesions 3
   • Bullous impetigo is caused exclusively by Staphylococcus aureus (unlike non-bullous impetigo which can also be caused by Streptococcus pyogenes) 1, 2

3. Bacterial culture indications:

   • When MRSA is suspected
   • In cases of treatment failure
   • During outbreaks
   • In immunocompromised patients 1

Differential Diagnosis

• Non-bullous impetigo
• Autoimmune blistering diseases
• Thermal burns
• Contact dermatitis
• Herpes simplex infection
• Varicella zoster infection
• Staphylococcal scalded skin syndrome (SSSS) 4

Key Diagnostic Distinctions

• Bullous impetigo vs. SSSS:

  • In bullous impetigo: exfoliative toxins are restricted to the area of infection, and bacteria can be cultured from blister contents
  • In SSSS: exfoliative toxins spread hematogenously, causing widespread epidermal damage at distant sites 5

• Bullous impetigo vs. Non-bullous impetigo:

  • Bullous: larger blisters, caused exclusively by S. aureus
  • Non-bullous: smaller pustules, can be caused by S. aureus or S. pyogenes 2

Diagnostic Pitfalls to Avoid

1. Failure to consider MRSA:

   • Community-acquired MRSA is an increasing concern as an etiological agent 1
   • Consider MRSA particularly in recalcitrant cases

2. Inadequate sampling:

   • Surface swab cultures may miss deeper infection
   • Ensure proper collection of fluid from intact bullae when possible

3. Missing carrier status:

   • In outbreak settings, remember to check for asymptomatic carriers
   • Nasal swabs from patients and close contacts may identify carriers 5, 6

4. Overlooking complications:

   • While rare, poststreptococcal glomerulonephritis can occur
   • Monitor for systemic symptoms in extensive cases 1, 2

Special Considerations

• In neonates and infants, bullous impetigo can spread rapidly and may be confused with other conditions 7
• In healthcare settings, consider asymptomatic healthcare workers as potential sources in outbreak situations 6
• For recurrent cases, investigate potential nasal carriage in the patient or family members 5

By following this diagnostic approach, clinicians can accurately identify staph bullous impetigo and initiate appropriate treatment promptly to prevent complications and transmission.