Impetigo: Signs, Symptoms, Treatment, and Risk Factors
Clinical Presentation and Signs/Symptoms
Impetigo is a highly contagious superficial bacterial skin infection characterized by honey-colored crusted lesions on the face and extremities in its nonbullous form, or large flaccid bullae in its bullous variant. 1
Nonbullous Impetigo (70% of cases)
- Presents with honey-colored crusts on the face and extremities 2
- May primarily affect intact skin or secondarily infect insect bites, eczema, or herpetic lesions 2
- Caused by Staphylococcus aureus and/or Streptococcus pyogenes 1, 2
Bullous Impetigo (30% of cases)
- Characterized by large, flaccid, fluid-filled bullae and blisters 2, 3
- More likely to affect intertriginous areas (skin folds) 2
- Caused exclusively by S. aureus producing exfoliative toxins 3
General Features
- Both types typically resolve within 2-3 weeks without scarring 2
- The infection affects the superficial epidermal and dermal layers 4
Risk Factors
Age-Related Risk
- Most commonly affects children 2-5 years of age 1, 2
- Incidence decreases with age 5
- Neonates and infants under 5 years are particularly susceptible to bullous impetigo and staphylococcal scalded skin syndrome 3
Predisposing Conditions
- Pre-existing skin conditions: eczema, insect bites, herpetic lesions 2
- Breaks in skin integrity allowing bacterial entry 2
- Close contact settings (schools, nurseries) due to high contagiousness 5, 6
Treatment Algorithm
For Limited/Localized Disease: Topical Antibiotics First-Line
Mupirocin 2% ointment applied three times daily for 5-7 days is the first-line treatment for limited impetigo lesions. 1, 7
- Mupirocin is FDA-approved for impetigo caused by S. aureus and S. pyogenes 7
- Alternative: Retapamulin 1% ointment applied twice daily for 5 days 1
- Topical therapy may be superior to oral antibiotics for limited disease 6
For Extensive Disease: Oral Antibiotics
Oral antibiotics are indicated when impetigo is extensive, involves multiple sites, topical therapy is impractical, topical treatment has failed, or systemic symptoms are present. 1, 8
First-Line Oral Agents (for MSSA)
- Dicloxacillin 250 mg four times daily (adults) 8
- Cephalexin 250-500 mg four times daily (adults) 8
- Dosing should be adjusted by weight for children 8
For Suspected or Confirmed MRSA
- Clindamycin 300-450 mg three times daily (adults) 8
- Trimethoprim-sulfamethoxazole (TMP-SMX) 1, 8
- Doxycycline (not for children under 8 years) 8
Treatment Duration
- Topical antibiotics: 5-7 days 1, 8
- Oral antibiotics: 5-10 days 8
- Complete the full course even if symptoms improve quickly to prevent complications such as post-streptococcal glomerulonephritis 1
Special Considerations for MRSA
Consider empiric therapy for community-acquired MRSA in patients at risk, those failing first-line therapy, or in areas with high local MRSA prevalence. 1
- Obtain cultures if treatment failure occurs, MRSA is suspected, or in recurrent infections 8
- Antimicrobial therapy should be active against both S. aureus and streptococci 8
Common Pitfalls and Caveats
Critical Treatment Errors to Avoid
- Penicillin alone is not effective for impetigo as it lacks adequate coverage against S. aureus 8, 6
- Do not use topical disinfectants—they are inferior to antibiotics 2, 6
- Avoid TMP-SMX monotherapy unless streptococcal infection is definitively ruled out by culture, as it provides inadequate streptococcal coverage 9, 2
- Tetracyclines (doxycycline, minocycline) should not be used in children under 8 years of age 8
When to Reassess
- Re-evaluate if no improvement after 48-72 hours of therapy 8, 9
- If impetigo is not responding to appropriate therapy, consider alternative diagnoses 8
- Consider MRSA coverage or obtain cultures to guide therapy adjustment 8, 9