What is impetigo, its clinical presentation, and the recommended treatment, including alternatives for penicillin‑allergic patients?

Impetigo: Clinical Presentation and Treatment

Impetigo should be treated with topical mupirocin 2% ointment twice daily for 5 days when disease is limited, or oral cephalexin/dicloxacillin for 7 days when disease is extensive, with clindamycin or trimethoprim-sulfamethoxazole reserved for MRSA coverage or penicillin-allergic patients. 1

What is Impetigo?

Impetigo is a highly contagious bacterial infection of the superficial layers of the epidermis, predominantly affecting children and representing one of the most common skin and soft tissue infections worldwide. 2 The disease has a global burden exceeding 140 million cases, with incidence decreasing with age. 3

Clinical Presentation

Two distinct forms exist:

• Non-bullous impetigo (70% of cases): Characterized by discrete purulent lesions with distinctive honey-colored crusted lesions, caused by β-hemolytic Streptococcus species and/or Staphylococcus aureus. 2, 3

• Bullous impetigo (30% of cases): Presents with fragile fluid-filled vesicles and flaccid blisters, exclusively caused by toxin-producing S. aureus. 1, 4

Physical examination reveals erythema, tenderness, and induration at affected sites. 2 Diagnosis is primarily clinical based on the characteristic appearance, though bacterial culture can confirm pathogens and guide therapy when needed. 3, 5

Treatment Algorithm

For Limited Disease (Few Lesions)

Topical therapy is first-line and superior to oral antibiotics:

• Mupirocin 2% ointment applied twice daily for 5 days achieves cure rates 6-fold higher than placebo and is highly effective. 1, 6

• Retapamulin 1% ointment applied twice daily for 5 days is an alternative for patients aged 9 months or older (covering up to 100 cm² in adults or 2% total body surface area in children). 1

Topical therapy successfully treats more than 90% of superficial, localized cases and is superior in eradicating S. aureus, including antibiotic-resistant strains. 7, 6

For Extensive Disease (Numerous Lesions or Outbreaks)

Oral antibiotics are required for 7 days (not the shorter 5-day topical course):

First-Line Oral Therapy (Presumed MSSA):

• Cephalexin: 250-500 mg four times daily for adults; 25-50 mg/kg/day divided into 4 doses for children, for 7 days. 1

• Dicloxacillin: 250 mg four times daily for adults; 25-50 mg/kg/day divided into 4 doses for children, for 7 days. 1

• Co-amoxiclav (amoxicillin-clavulanic acid): An acceptable alternative providing coverage for both S. aureus and S. pyogenes, dosed for 7 days. 1

When MRSA is Suspected or Confirmed:

Community-acquired MRSA is an emerging concern as an etiological agent for impetigo. 2 Empiric MRSA coverage should be initiated for patients at risk or who fail first-line therapy. 2

• Clindamycin: 300-450 mg three to four times daily for adults; 20-30 mg/kg/day divided into 3 doses for children, for 7 days. 1

• Trimethoprim-sulfamethoxazole (TMP-SMX): 1-2 double-strength tablets twice daily for adults; 8-12 mg/kg/day (trimethoprim component) divided into 2 doses for children, for 7 days. 1

• Doxycycline: For children over 8 years old only, 2-4 mg/kg/day divided into 2 doses for 7 days. 1

Management of Penicillin-Allergic Patients

For patients with penicillin allergy:

• Cephalexin can be used except in those with immediate hypersensitivity reactions (anaphylaxis, urticaria). 1

• Clindamycin is the preferred alternative: 300-450 mg three to four times daily for adults; 20-30 mg/kg/day divided into 3 doses for children. 1

• Macrolides can be considered, though resistance rates to erythromycin are rising significantly. 2, 5

Critical Treatment Pitfalls to Avoid

Penicillin alone is seldom effective and should only be used when cultures confirm streptococci alone, as S. aureus is now the predominant causative organism. 1, 5

Amoxicillin alone should not be used because it lacks adequate coverage against S. aureus. 1

Oral antibiotics require 7 days of treatment, not the shorter 5-day course used for topical agents, to avoid treatment failure. 1

Tetracyclines (doxycycline) must be avoided in children under 8 years due to the risk of permanent dental staining. 1

Topical disinfectants are not useful as primary therapy, with little evidence they improve outcomes. 1, 5

Infection Control and Adjunctive Measures

To prevent spread and recurrence:

• Keep lesions covered with clean, dry bandages. 1

• Maintain good personal hygiene with regular handwashing. 1

• Avoid sharing personal items that contact the skin (towels, clothing, razors). 1

• Apply plain petrolatum ointment and bandages over open erosions after bullae have deroofed. 1

For recurrent impetigo: Evaluate for nasal carriage of S. aureus in the patient and immediate family members, as the nasal epithelium serves as a reservoir for skin colonization. 7, 4

Special Populations

Pregnant patients: Cephalexin can be considered a safe alternative. 1

Immunocompromised or diabetic patients: May have more severe or spreading lesions requiring systemic antibiotics, with a lower threshold for hospital admission if extensive disease or systemic signs are present. 1

During outbreaks of poststreptococcal glomerulonephritis: Systemic antimicrobials should be used to eliminate nephritogenic strains. 1