Clinical Overview

Impetigo is a highly contagious superficial bacterial infection affecting children (peak incidence 2-6 years), caused predominantly by Group A Streptococcus pyogenes and/or Staphylococcus aureus. The condition presents with characteristic honey-colored (golden-yellow) crusts overlying erosions on erythematous base, typically on face, extremities, or other exposed areas. Two clinical forms exist: nonbullous impetigo (70-80% of cases) with characteristic honey crusts, and bullous impetigo (20-30% of cases) with flaccid bullae that rupture leaving thin erosions. The condition is highly contagious through direct contact with lesion fluid or respiratory secretions; untreated patients can transmit infection for weeks. Impetigo typically develops following break in skin barrier (insect bite, trauma, other dermatitis) or in settings of poor hygiene or overcrowding. Early recognition and appropriate antibiotics are essential to prevent transmission and rare complications including acute post-streptococcal glomerulonephritis or acute rheumatic fever (now rare with antibiotics but still possible).

Epidemiology

Impetigo affects approximately 111-150 million children annually worldwide, representing the most common bacterial skin infection in children in developed nations and endemic in tropical/developing regions. Peak incidence occurs 2-6 years of age. Male predominance is slight (1.2:1). Geographic and seasonal variation is substantial: higher prevalence in warm climates and summer months. Risk factors include: poor hygiene, overcrowding, low socioeconomic status, trauma or break in skin barrier, warm/humid environment, underlying skin conditions (atopic dermatitis, scabies), and recent streptococcal infection. Causative organisms have evolved: historically, Group A Streptococcus was predominant (particularly in tropical regions), but Staphylococcus aureus (including MRSA) increasingly causes impetigo in developed nations. Streptococcal impetigo shows higher association with post-infectious glomerulonephritis (3-5% of cases), while staphylococcal impetigo shows higher association with recurrence and chronic carrier state.

Pathophysiology

Impetigo develops when Group A Streptococcus or Staphylococcus aureus colonize and invade epidermis through break in skin barrier. The bacteria produce virulence factors and exotoxins (streptococcal pyrogenic exotoxins, staphylococcal alpha-toxins) causing damage to keratinocytes and contributing to inflammatory response. Local immune response with neutrophil infiltration is visible as pustules and exudation. The characteristic honey-colored crusts result from oxidized hemoglobin and protein in dried exudate. Histologically, subcorneal pustules (collections of neutrophils within epidermis) are characteristic of impetigo, distinguishing from deeper folliculitis. In bullous impetigo, exfoliative toxins (exfoliative toxin A and B produced primarily by staphylococci) cause acantholysis (separation of epidermal cells) with blister formation. Post-infectious complications including acute glomerulonephritis can develop 1-3 weeks after streptococcal impetigo through immune complex deposition in glomeruli, though this is now rare with appropriate antibiotics.

Clinical Presentation

Nonbullous impetigo (most common form) presents with erythematous papules that rapidly progress to pustules and then rupture, leaving characteristic honey-colored or golden-yellow adherent crusts on erythematous base. Lesions typically are 0.5-2 cm in diameter. Surrounding erythema may be present. Pruritus is common. Common sites include face (particularly around nose and mouth), exposed extremities, and areas of trauma. Regional lymphadenopathy (particularly anterior cervical and submandibular nodes) is frequent. Bullous impetigo presents with flaccid bullae (thin-walled, easily ruptured) containing clear or slightly turbid fluid, which rupture leaving thin erosions and characteristic moist appearance without crusting. Bullous impetigo more commonly affects intertriginous areas. Systemic symptoms are usually absent in uncomplicated impetigo; however, fever may be present if significant regional lymphadenitis develops. Secondary complications including cellulitis progression, abscess formation, or systemic infection are uncommon but possible. The course without treatment is one of gradual progression with new lesions developing over weeks; spontaneous resolution may occur over several weeks to months.

Diagnosis

Diagnosis is primarily clinical based on characteristic honey-colored crusts on erythematous base. Key diagnostic features include: (1) honey-colored crusts on erosions; (2) erythematous base; (3) typical location on exposed areas; (4) typical age group (children); (5) contagion history. Gram stain or bacterial culture of crusts or fluid obtained after crust removal confirms organism identification and guides antibiotic selection and allows MRSA detection. Cultures are particularly helpful for treatment-resistant cases or for determining organism prevalence in specific regions. White/golden crusts may help distinguish from other bacterial skin infections. Differential diagnosis includes: staphylococcal folliculitis (involves hair follicles, not superficial epidermis), contact dermatitis (lacks pustules and crusts), viral infection (HSV shows vesicles, different history), and scabies (itching more intense, other features present).

Treatment Algorithm

Treatment of impetigo combines topical and systemic antibiotics depending on extent and severity. Impetigo without complicating factors (non-severe, limited number of lesions) can be managed with topical antibiotics in many regions, though systemic antibiotics provide more reliable cure and faster symptom resolution.

Topical antibiotics for localized impetigo: mupirocin 2% ointment applied 2-3 times daily for 5-10 days is effective for limited lesions (< 5 lesions, <5% body surface area); alternatively, retapamulin 1% ointment once or twice daily for 5 days is effective. Crust removal before topical application improves efficacy. However, topical antibiotics alone have higher failure/relapse rates compared to systemic therapy.

Systemic antibiotics are appropriate for: (1) extensive impetigo (>5 lesions, >5% body surface area); (2) bullous impetigo; (3) facial involvement; (4) failure of topical therapy; (5) systemic toxicity. First-line systemic agent: oral amoxicillin-clavulanate 40-45 mg/kg/day divided into two to three doses (total dose not exceeding adult dose 500-875 mg twice daily) for 7-10 days (covers both streptococcus and staphylococcus). Alternative agents for penicillin allergy: oral clindamycin 30 mg/kg/day divided three times daily, or azithromycin 12 mg/kg/day once daily (though resistance is increasing). For MRSA suspected/confirmed: clindamycin or trimethoprim-sulfamethoxazole. If systemic symptoms suggest deeper infection (cellulitis), intravenous antibiotics may be necessary.

Supportive care: remove crusts with warm saline soaks before topical application, keep lesions clean and covered to prevent transmission, practice good hand hygiene, avoid direct contact with others until lesions crust over or 24 hours of antibiotics completed. Avoid environmental spread through separate towels and personal items.

Prognosis

The prognosis of impetigo with appropriate antibiotic therapy is excellent: cure rates exceed 95% with systemic therapy. Factors influencing outcomes include: timely initiation of antibiotics (early treatment prevents complications and transmission), adequate treatment duration (full course completion reduces relapse risk of 5-15%), organism type (streptococcal impetigo shows lower relapse rates than staphylococcal), and elimination of transmission sources. Post-infectious glomerulonephritis occurs in 1-5% of streptococcal impetigo cases despite antibiotic treatment, though this is becoming rare with modern antibiotics. Recurrence rates of 10-20% occur if predisposing factors (poor hygiene, chronic skin disease, carrier state) are not addressed.

When to See a Dermatologist

Evaluation by primary care is typical; dermatology referral is appropriate for: (1) diagnostic uncertainty; (2) recurrent/chronic impetigo; (3) failure of appropriate therapy; (4) complications suggesting deeper infection.

Frequently Asked Questions

Q: Is impetigo contagious? A: Yes, impetigo is highly contagious through direct contact with lesion fluid. Untreated patients can transmit infection for weeks. Patients on appropriate antibiotics become non-contagious after 24-48 hours.

Q: When can my child return to school/daycare? A: Most schools require 24-48 hours of appropriate antibiotic therapy before return. Lesions should be covered with bandages to prevent direct contact transmission. Contact school/daycare for specific requirements.

Q: Can impetigo lead to serious complications? A: Serious complications are uncommon with appropriate antibiotics. Potential complications include post-streptococcal glomerulonephritis (now rare with treatment) and acute rheumatic fever (extremely rare). Cellulitis progression is possible if untreated.

Q: What causes impetigo to recur? A: Recurrence may result from: inadequate initial treatment, reinfection from untreated contacts, carrier state (bacteria colonizing skin or nasopharynx), underlying skin disease, or poor hygiene.

References

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