How is impetigo treated, considering eosinophil count status?

Treatment of Impetigo: Considerations for Eosinophil Count Status

Topical mupirocin ointment is the first-line treatment for localized impetigo regardless of eosinophil count status, while oral antibiotics should be used for extensive disease, with specific antibiotic selection guided by suspected pathogen and patient factors.

Understanding Impetigo and Eosinophil Count

Impetigo is a highly contagious bacterial skin infection that presents in two main forms:

• Nonbullous impetigo (70% of cases): Caused by Staphylococcus aureus or Streptococcus pyogenes, characterized by honey-colored crusts 1
• Bullous impetigo (30% of cases): Caused exclusively by S. aureus, characterized by large, flaccid bullae 1

Eosinophil count status is not typically a consideration in the diagnosis or management of impetigo, as this infection is bacterial in nature and does not typically cause eosinophilia. However, if eosinophilia is present, it may indicate:

1. An unrelated parasitic infection
2. An allergic reaction
3. Other underlying conditions

Treatment Algorithm for Impetigo

Step 1: Assess Extent of Disease

• Limited/localized disease: Few lesions in a small area
• Extensive disease: Multiple lesions or large affected areas

Step 2: Select Treatment Based on Extent

For Limited/Localized Disease:

• First-line: Topical mupirocin 2% ointment applied three times daily for 7-10 days 1, 2

  • Clinical efficacy rates: 71-93% 2
  • Pathogen eradication rates: 94-100% 2
  • Effective against both S. aureus and S. pyogenes 1

• Alternatives:

  • Retapamulin or fusidic acid if available 1

For Extensive Disease:

• First-line oral options:
  • For suspected MSSA or streptococcal infection: Cephalexin 250 mg four times daily (adults) or 25-50 mg/kg/day in 3-4 divided doses (children) for 7 days 1
  • For suspected MRSA: Clindamycin 300 mg three times daily for 7-10 days 1
  • For broader coverage: Amoxicillin/clavulanate 500/125 mg three times daily or 875/125 mg twice daily for 7-10 days 1

Step 3: Special Considerations

For Penicillin-Allergic Patients:

• Non-immediate hypersensitivity: Can still use cephalexin
• Immediate hypersensitivity: Use clindamycin 300-400 mg four times daily 1

For Children:

• Avoid tetracyclines (doxycycline, minocycline) in children under 8 years 1
• Mupirocin is safe and effective in children as young as 2 months 2

For Patients with Elevated Eosinophil Count:

If a patient with impetigo has an elevated eosinophil count (>0.45 × 10⁹/L), consider:

1. Treating impetigo as usual - The eosinophilia is likely unrelated to the bacterial skin infection
2. Additional investigation for potential parasitic infections or other causes of eosinophilia 3
   • Consider stool examination for ova and parasites
   • Consider serology for parasitic infections based on travel history

Monitoring and Follow-up

• Evaluate clinical response within 48-72 hours 1
• Expected resolution within 7-10 days of starting appropriate treatment 1
• If no improvement is seen within 3-5 days:
  • Obtain bacterial culture and sensitivity testing
  • Consider alternative diagnosis
  • Evaluate for possible MRSA infection 1

Important Considerations

• Eosinophilia in a patient with impetigo should prompt investigation for other causes, as impetigo itself does not typically cause eosinophilia 3
• Prevention measures are essential to avoid spread:
  • Keep lesions covered when possible
  • Use separate towels and linens
  • Practice good hand hygiene
  • Change clothing that contacts affected areas daily 1
• Complications of impetigo are rare, with poststreptococcal glomerulonephritis being the most serious (<1 case/1,000 population per year) 1

Common Pitfalls to Avoid

1. Failing to consider MRSA as the causative organism in recalcitrant impetigo
2. Using penicillin alone, which is inferior to other antibiotics for impetigo
3. Inadequate duration of therapy
4. Relying solely on topical therapy for extensive disease
5. Not addressing underlying conditions that may predispose to recurrent infection 1
6. Attributing eosinophilia to impetigo when it likely indicates a separate condition requiring investigation 3

In summary, the management of impetigo is not directly affected by eosinophil count status, but elevated eosinophils should prompt additional investigation for other potential causes while treating the impetigo according to standard guidelines.