What is impetigo?

Impetigo: A Highly Contagious Bacterial Skin Infection

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

Types and Clinical Presentation

There are two principal types of impetigo:

1. Nonbullous Impetigo (70% of cases):

   • Caused by S. aureus or S. pyogenes
   • Begins as papules that rapidly evolve into vesicles surrounded by erythema
   • Vesicles become pustules that break down over 4-6 days
   • Forms characteristic honey-colored crusts on the face and extremities
   • May develop as a primary infection or secondary to insect bites, eczema, or other skin conditions 1

2. Bullous Impetigo (30% of cases):

   • Caused exclusively by toxin-producing strains of S. aureus
   • Presents as superficial vesicles that rapidly enlarge to form flaccid bullae
   • Bullae contain clear yellow fluid that later becomes darker and turbid
   • Bullae may rupture, leaving thin brown crusts resembling lacquer
   • More likely to affect intertriginous areas 1, 2

Pathophysiology

• Colonization with streptococcal strains precedes impetigo development by approximately 10 days
• Bacteria enter the skin through abrasions, minor trauma, or insect bites
• In staphylococcal impetigo, pathogens typically colonize the nasal epithelium before causing cutaneous disease
• In bullous impetigo, S. aureus produces exfoliative toxins that target desmoglein-1, resulting in characteristic bullous lesions 1, 2

Diagnosis

Diagnosis is primarily clinical based on the characteristic appearance of lesions. Key features include:

• Exposed areas of the body (face and extremities) most commonly affected
• Well-localized but frequently multiple lesions
• Regional lymphadenitis may occur, but systemic symptoms are usually absent 1

Treatment

Topical Treatment

• First-line treatment for limited impetigo is topical mupirocin applied twice daily for 5 days 2, 3
• Clinical efficacy rates for mupirocin are significantly higher (71-93%) compared to placebo (35%) 3
• Retapamulin is an alternative topical option 2

Systemic Treatment

• For extensive disease, a 7-day regimen with an oral antibiotic active against the causative organisms is recommended:
  • For MSSA: Dicloxacillin or cephalexin
  • For suspected MRSA: Doxycycline, clindamycin, or trimethoprim/sulfamethoxazole 2
• Penicillin alone is not effective for impetigo treatment 1

Prognosis and Complications

• Typically resolves within 2-3 weeks without scarring
• May leave temporary depigmented areas
• Complications are rare, with poststreptococcal glomerulonephritis being the most serious potential complication 4

Prevention

• Avoid close contact with infected individuals
• Maintain good hygiene practices
• Consider evaluation for S. aureus carriage in patients with recurrent impetigo 5

Special Considerations

• Rising rates of antibiotic-resistant bacteria (MRSA, macrolide-resistant streptococcus, and mupirocin-resistant strains) may influence treatment decisions 4
• For bullous impetigo that is widespread, systemic antibiotics are preferred over topical treatment 6
• Topical disinfectants are inferior to antibiotics and should not be used 7

Impetigo's high contagiousness, especially among children in crowded living conditions, makes prompt diagnosis and treatment essential to prevent spread and reduce the clinical course of this common skin infection.