What is impetigo?

Impetigo: Clinical Description and Management

Impetigo is a highly contagious bacterial infection of the superficial layers of the epidermis, predominantly affecting children, characterized by discrete purulent lesions caused by β-hemolytic Streptococcus species and/or Staphylococcus aureus. 1

Clinical Presentation

Types of Impetigo

• Nonbullous impetigo (70% of cases)

  • Characterized by honey-colored crusts on face and extremities
  • Caused by S. aureus or Streptococcus pyogenes 2

• Bullous impetigo (30% of cases)

  • Characterized by large, flaccid bullae
  • Caused exclusively by S. aureus
  • More likely to affect intertriginous areas 2

Physical Examination Findings

• Erythema, tenderness, and induration 1
• Discrete purulent lesions 1
• Honey-colored crusts (nonbullous type) 2
• Fragile fluid-filled vesicles and flaccid blisters (bullous type) 3

Epidemiology

• Most common in children 2-5 years of age 2
• Global disease burden exceeds 140 million cases 4
• Incidence decreases with age 4
• Community-acquired MRSA (CA-MRSA) is an increasing concern as an etiological agent 1

Diagnosis

• Primarily clinical based on characteristic appearance 4
• Culture of lesions can confirm diagnosis and determine antibiotic sensitivities 3
• Important to differentiate from other skin conditions such as eczema or herpetic lesions 2

Treatment

Topical Therapy

• For limited lesions, topical mupirocin is the treatment of choice (A-I evidence) 1, 5

  • Apply three times daily for 7-10 days
  • Clinical efficacy rates of 71-93% 5
  • Pathogen eradication rates of 94-100% 5

• Alternative topical options:

  • Retapamulin (less resistance reported) 6
  • Fusidic acid (not widely available in US) 1

Oral Antibiotic Therapy

• Indicated for:

  • Numerous lesions
  • Patients not responding to topical agents (A-I evidence) 1
  • Extensive disease 2

• First-line oral options:

  • Penicillinase-resistant semisynthetic penicillin (e.g., dicloxacillin)
  • First-generation cephalosporin (e.g., cephalexin) (A-I evidence) 1

• For penicillin-allergic patients:

  • Clindamycin
  • Macrolides (note: increasing resistance trends) 1

Special Considerations for MRSA

• For suspected or confirmed CA-MRSA:
  • Consider empiric therapy with agents effective against MRSA (A-I evidence) 1
  • Options include trimethoprim-sulfamethoxazole (note: inadequate for streptococcal coverage) 2
  • Clindamycin (be aware of potential for inducible resistance) 1

Complications

• Generally rare 4
• Poststreptococcal glomerulonephritis (rare in developed countries: <1 case/1,000 population per year) 1
  • Note: No data demonstrate that treatment of impetigo prevents this sequela 1

Treatment Pearls and Pitfalls

Pearls:

• Topical antibiotics are as effective as oral antibiotics for limited disease and have fewer side effects 6
• Mupirocin has shown slightly superior efficacy compared to oral erythromycin in clinical studies 6
• Re-evaluate patients in 24-48 hours if using tetracyclines or trimethoprim-sulfamethoxazole to verify clinical response 1

Pitfalls:

• Penicillin alone is inferior to erythromycin and cloxacillin for impetigo treatment 6
• Topical disinfectants are inferior to antibiotics and should not be used 6
• Growing resistance to commonly used antibiotics including mupirocin, macrolides, and methicillin 2
• Failure to identify and treat asymptomatic carriers in household contacts can lead to recurrence 3

Prevention

• Good hygiene practices
• Prompt treatment of cases to prevent spread
• Consider nasal swabs from patients and immediate family members to identify asymptomatic carriers of S. aureus 3