What are the typical areas involved, morphology, and treatment for impetigo?

Impetigo: Areas Involved, Morphology, and Treatment

Impetigo typically affects exposed areas of the body, most commonly the face and extremities, and is best treated with topical mupirocin or retapamulin for limited lesions, while oral antibiotics are recommended for extensive disease. 1, 2

Areas Involved

• Impetigo most frequently affects exposed areas of the body, particularly the face and extremities 1
• The peak incidence is among children aged 2-5 years, though older children and adults may also be affected 1, 3
• In staphylococcal impetigo, bullous lesions are more likely to affect intertriginous areas 3

Morphology

Impetigo presents in two main forms:

Nonbullous Impetigo (70% of cases)

• Begins as erythematous papules that rapidly evolve into vesicles and pustules 1
• These vesicles rupture, forming characteristic honey-colored crusts on an erythematous base 1, 3
• Caused by Staphylococcus aureus and/or Streptococcus pyogenes 2, 3

Bullous Impetigo (30% of cases)

• Appears initially as superficial vesicles that rapidly enlarge to form flaccid bullae 1
• Bullae contain clear yellow fluid that later becomes darker, more turbid, and sometimes purulent 1
• When bullae rupture, they often leave a thin brown crust resembling lacquer 1
• Caused exclusively by Staphylococcus aureus 3, 4

Ecthyma

• A deeper form of impetigo that extends through the epidermis into the dermis 1
• Begins as vesicles that rupture, resulting in circular, erythematous ulcers with adherent crusts 1
• Unlike regular impetigo, ecthyma heals with scarring 1

Treatment

First-Line Treatment: Topical Antibiotics

• For limited lesions, topical antibiotics are recommended: 2, 5
  • Mupirocin 2% ointment applied three times daily for 5-7 days 2, 6
  • Retapamulin 1% ointment applied twice daily for 5 days 2
• Topical mupirocin has shown clinical efficacy rates of 71-93% in clinical trials 6
• Topical antibiotics have fewer side effects compared to oral antibiotics 5

Second-Line Treatment: Oral Antibiotics

• Oral antibiotics are indicated for: 2, 3
  • Extensive disease
  • When topical therapy is impractical
  • Failure of topical treatment
  • Presence of systemic symptoms
• Recommended oral antibiotics include:
  • Dicloxacillin or first-generation cephalosporins (e.g., cephalexin) 2, 3
  • For suspected MRSA: trimethoprim-sulfamethoxazole, clindamycin, or doxycycline 2, 3
  • Note: Penicillin V is seldom effective for impetigo 3, 5

Special Considerations

• Complete the full course of prescribed antibiotics even if symptoms improve quickly 2
• Consider empiric therapy for CA-MRSA in patients at risk or in areas with high prevalence 2
• Cultures should be obtained when there is treatment failure or in outbreak settings 1
• Regional lymphadenitis may occur, but systemic symptoms are usually absent 1

Common Pitfalls and Caveats

• Topical disinfectants are inferior to antibiotics and should not be used 3, 5
• Increasing antibiotic resistance is a concern, particularly for MRSA, macrolide-resistant streptococci, and mupirocin-resistant strains 3
• Untreated impetigo usually resolves within 2-3 weeks but treatment helps prevent spread and complications such as post-streptococcal glomerulonephritis 3, 7
• For bullous impetigo, it's important to identify and treat asymptomatic nasal carriers of S. aureus among close contacts 4