Impetigo

What is it?

Impetigo is a highly contagious bacterial skin infection that predominantly affects the superficial layers of the skin (epidermis). It presents as honey-colored crusted lesions or fluid-filled blisters (vesicles and bullae) that rupture easily, most commonly appearing on the face and extremities.

Who is affected?

Impetigo is the most common bacterial skin infection in children, particularly affecting those aged 2 to 5 years. The condition accounts for approximately 10% of all skin-related complaints in pediatric populations.

• Prevalence: Affects about 1 in 10 children (10%) seeking dermatological care
• Age demographics: Peak incidence in children 2-5 years; can occur at any age
• Gender distribution: Equal prevalence in male and female children; slightly more common in adult males
• Risk factors: Warm, humid climates; summer and fall seasons; close contact settings (schools, daycare); poor hygiene; pre-existing skin conditions (atopic dermatitis, insect bites); contact sports

What causes it?

Impetigo results from bacterial colonization and toxin production within the superficial skin layers:

• Primary pathogenic mechanisms: Caused predominantly by Staphylococcus aureus (approximately 80% of nonbullous cases; nearly 100% of bullous cases); Streptococcus pyogenes (Group A beta-hemolytic Streptococcus) accounts for 10% of nonbullous cases, with 10% involving both organisms
• Contributing factors: Disruption of the skin barrier through minor trauma, abrasions, insect bites, or pre-existing dermatoses (skin conditions) allows bacterial entry and proliferation
• Triggering elements: Warm, humid weather; crowded living conditions; poor hygiene; contact with infected individuals or contaminated fomites (objects)
• Toxin production: In bullous impetigo, S. aureus produces exfoliative toxins (epidermolytic toxins) that cleave desmosomal proteins (cellular adhesion molecules), causing intraepidermal blister formation

What are the clinical features?

Impetigo presents in two principal forms with distinct characteristics:

• Nonbullous impetigo (70% of cases): Small vesicles (fluid-filled bumps) that rapidly rupture, leaving characteristic honey-colored or golden crusts; lesions typically appear on exposed areas such as face, particularly around the nose and mouth, and on the extremities
• Bullous impetigo (30% of cases): Small vesicles that progress to larger, flaccid bullae (thin-walled blisters) containing clear to yellow fluid; bullae rupture easily, leaving a collarette of scale; more commonly affects skin folds (intertriginous areas) such as the axillae (armpits) and diaper region
• Disease progression: Lesions begin as small red macules (flat spots) that evolve into vesicles or pustules (pus-filled bumps) within hours to days; without treatment, new lesions may continue to develop through self-inoculation (spreading by touching)

How is it diagnosed?

Impetigo is primarily a clinical diagnosis based on characteristic appearance:

• Clinical assessment methods: Recognition of pathognomonic honey-colored crusts (in nonbullous form) or flaccid bullae with collarette scaling (in bullous form); evaluation of distribution pattern and patient demographics
• Common diagnostic tests: Bacterial culture and sensitivity testing may be performed for extensive infections, treatment failures, or suspected methicillin-resistant Staphylococcus aureus (MRSA); Gram stain can rapidly identify causative organisms
• Differential considerations: Nonbullous impetigo must be distinguished from herpes simplex virus infection, atopic dermatitis with secondary impetiginization, contact dermatitis, and tinea corporis; bullous impetigo requires differentiation from bullous pemphigoid, epidermolysis bullosa, and burns

What treatment options are available?

Treatment aims to eradicate infection, prevent spread, and minimize complications:

• First-line therapeutic approaches: Topical antibiotics (mupirocin 2% ointment, retapamulin 1% ointment) applied three times daily for 5-7 days for limited disease (fewer than five lesions); gentle removal of crusts with warm compresses facilitates antibiotic penetration
• Systemic therapy: Oral antibiotics indicated for bullous impetigo, extensive disease (more than five lesions), deep tissue involvement, or when topical therapy is impractical; options include cephalexin, dicloxacillin, amoxicillin-clavulanate, or clindamycin (for MRSA consideration)
• Lifestyle modifications and self-care: Maintain good hygiene; keep fingernails trimmed; avoid touching or scratching lesions; wash hands frequently; avoid sharing personal items (towels, clothing); exclude from school or daycare until 24 hours after initiating antibiotic therapy
• Prognosis and expected outcomes: Untreated impetigo typically resolves spontaneously within 14-21 days; with appropriate antibiotic therapy, resolution occurs within 7-10 days; scarring is uncommon; recurrence may occur in 10-15% of cases

Key points for patients

• Impetigo is highly contagious but responds well to antibiotic treatment
• Most cases resolve completely within 10 days with appropriate therapy, without leaving scars
• Complications are rare but may include cellulitis (deeper skin infection), lymphangitis (lymphatic inflammation), or post-streptococcal glomerulonephritis (kidney inflammation affecting approximately 5% of cases)
• When to seek medical attention: Fever, increasing pain, spreading redness beyond lesions, dark urine (suggesting kidney involvement), or failure to improve within 3-5 days of treatment
• Prevention strategies: Practice good hand hygiene; promptly clean and cover minor skin injuries; avoid close contact with infected individuals; do not share personal items; maintain clean living environments