Impetigo

Impetigo is the most common bacterial skin infection in children, caused by Group A Streptococcus (GAS) and/or Staphylococcus aureus. It presents in two forms: nonbullous (70%) and bullous (30%). Diagnosis is clinical; treatment is primarily topical antibiotics for mild disease and oral antibiotics for severe or multilesional cases. [1-3]

• Onset and progression: Erythematous papules progressing to vesicles/pustules or bullae that rupture over 4–6 days, forming characteristic honey-colored crusts [1]
• Location: Face and extremities (nonbullous); trunk and intertriginous areas such as axillae/groin (bullous) [1][3]
• Pruritus/pain: Lesions can be pruritic and painful; scratching promotes autoinoculation and satellite lesions [1]
• Preceding skin disruption: Insect bites, eczema, abrasions, herpetic lesions, scabies — impetigo commonly secondarily infects these [3-4]
• Contacts: Ask about similar lesions in household members, daycare, or school contacts (highly contagious) [1][5]
• Important negatives: Absence of fever and lymphadenopathy is typical; their presence should raise concern for deeper infection [1]

• Rapidly spreading erythema, warmth, or induration beyond the crusted lesion → concern for cellulitis or erysipelas [1]
• Deep ulceration with adherent crust and scarring → ecthyma (deeper infection requiring oral antibiotics) [2]
• Systemic toxicity (high fever, tachycardia, hypotension) → concern for necrotizing soft tissue infection or sepsis (rare) [1]
• Periorbital involvement → risk of orbital cellulitis
• Cola-colored urine, edema, or hypertension 1–3 weeks after streptococcal impetigo → poststreptococcal glomerulonephritis [1][6]
• Widespread bullous impetigo in neonates → consider staphylococcal scalded skin syndrome (SSSS)

Topical (mild, localized disease — first line)

• Mupirocin 2% ointment — apply BID × 5 days (first-line topical) [1-2]
• Retapamulin 1% ointment — apply BID × 5 days (≥9 months; note: rising resistance) [1-2]

Oral (severe, multilesional, or topical failure after 3–5 days):

• Cephalexin — Adults: 250 mg q6h; Children: 25–50 mg/kg/day divided TID-QID × 7–10 days (first-line oral in children) [1]
• Dicloxacillin — Adults: 250 mg q6h × 7–10 days (first-line oral in adults) [1]
• If MRSA suspected: Clindamycin 300 mg q6h (adults) or 20 mg/kg/day divided TID (children); TMP-SMX; or doxycycline (≥8 years) [1-2]

Contraindicated/Ineffective

• Oral penicillin alone is NOT effective for impetigo [3][6]
• Topical disinfectants are inferior to antibiotics and should not be used [3][6]

The following table from the AAFP summarizes treatment options with dosing:

• No specific dietary triggers or restrictions
• Adequate hydration and nutrition support immune function; malnutrition is a recognized risk factor for impetigo [1]

• Skin: New lesions elsewhere (autoinoculation), underlying eczema or dermatitis, recent insect bites or trauma
• Renal: Dark/cola-colored urine, decreased urine output, facial/periorbital edema (poststreptococcal glomerulonephritis)
• Constitutional: Fever, malaise (uncommon in uncomplicated impetigo — if present, consider deeper infection) [1]
• MSK: Joint pain or swelling (rare; rheumatic fever complication) [4]

• Contacts with similar skin lesions — daycare, school, household members, sports teams [1][5]
• History of recurrent skin infections in the patient or family (consider MRSA colonization, immunodeficiency, or underlying dermatosis)
• Social context: Crowded living conditions, homelessness, incarceration — all increase transmission risk [1]
• Atopic dermatitis in the family — predisposes to secondary impetiginization

• Age 2–5 years (peak incidence) [1][3]
• Disrupted skin barrier: Eczema, insect bites, abrasions, scabies, varicella [3-4]
• Poor hygiene and crowded living environments [1]
• Hot, humid climates (streptococcal forms predominate in tropical settings) [6]
• Malnutrition and diabetes [1]
• Contact sports (e.g., wrestling — "mat herpes" and impetigo outbreaks)

• Herpes simplex virus (HSV): Grouped vesicles on an erythematous base; Tzanck smear or PCR distinguishes
• Varicella: Diffuse vesicles in various stages ("crops"), systemic symptoms
• Contact dermatitis: Pruritic, well-demarcated; no honey-colored crust; history of exposure
• Tinea corporis: Annular, scaly plaque with central clearing; KOH positive
• Scabies with secondary impetiginization: Burrows, interdigital involvement, intense nocturnal pruritus [4]
• Staphylococcal scalded skin syndrome (SSSS): Widespread erythema and desquamation in neonates/young children; Nikolsky sign positive
• Ecthyma: Deeper ulcerative lesions with thick crust and scarring (a complication/extension of impetigo) [2]
• Pemphigus/bullous pemphigoid: Consider in adults with bullous lesions unresponsive to antibiotics

• Atopic dermatitis/eczema — most common predisposing condition for secondary impetigo [3]
• Previous episodes of impetigo — recurrence suggests persistent colonization (consider nasal mupirocin decolonization)
• Immunocompromised states — HIV, chemotherapy, chronic corticosteroid use
• Diabetes mellitus [1]
• History of MRSA infection or colonization — guides empiric antibiotic choice [2]

• Nonbullous: Erythematous papules → vesicles/pustules → honey-colored crusts on an erythematous base, typically on face and extremities [1-2]
• Bullous: Large, flaccid bullae with clear-to-yellow fluid; collarettes of scale at periphery of ruptured bullae; favors trunk and intertriginous areas [1][3]
• Satellite lesions from autoinoculation [1]
• Regional lymphadenopathy: Uncommon; if present, consider deeper or more extensive infection [1]
• Assess for: Surrounding cellulitis (spreading erythema, warmth, induration), signs of ecthyma (deep ulceration with scarring), and underlying dermatosis (eczema, scabies) [1][4]
• In skin of color: Erythema may be subtle; look for crusting, erosions, and post-inflammatory dyspigmentation [4]

• Routine cases: No labs needed; diagnosis is clinical [1]
• Culture and Gram stain of vesicle fluid/exudate: Recommended by IDSA but not required for typical presentations; obtain if treatment failure, recurrence, or diagnostic uncertainty [1-2]
• If poststreptococcal glomerulonephritis suspected: Urinalysis (hematuria, proteinuria), BMP (creatinine, BUN), complement levels (low C3), anti-DNase B (more sensitive than ASO for skin streptococcal infections) [1]
• ASO titer: Not helpful for diagnosing impetigo itself, but useful if poststreptococcal complications are suspected [1]

• Not indicated for uncomplicated impetigo
• Ultrasound: Consider if concern for underlying abscess (fluctuant area beneath crusted lesion)
• CT/MRI: Only if concern for necrotizing soft tissue infection or deep space infection (rare)

• Wound culture with sensitivities: Most useful special test when empiric therapy fails or MRSA is suspected [2]
• KOH preparation: To rule out tinea if annular or scaly morphology
• Tzanck smear or HSV PCR: If vesicular lesions raise concern for herpes simplex
• Dermoscopy: Can help differentiate from other vesiculobullous conditions

• Not routinely indicated
• Consider if concern for acute rheumatic fever (prolonged PR interval) as a rare complication of streptococcal impetigo [4]

Severity stratification

• Mild: ≤5 localized lesions, no systemic symptoms → topical therapy [1]
• Moderate-severe: >5–6 lesions, multilesional, or outbreak setting → oral antibiotics [1-2]
• Complicated: Progression to ecthyma, cellulitis, abscess, or systemic toxicity → escalate care [1]

Typical presentation: Afebrile child with honey-colored crusted lesions on the face, often with a history of preceding skin break. Resolves within 2–3 weeks without scarring even untreated, though ~25% show no improvement without antibiotics. [1][3]

Complications (rare but important)

• Ecthyma, cellulitis, erysipelas, abscess, necrotizing fasciitis [1]
• Poststreptococcal glomerulonephritis (antibiotics may not prevent this) [1][6]
• Acute rheumatic fever (antibiotics do prevent this) [1][4]
• Guttate psoriasis, scarlet fever [6]

Initial management

• Gentle wound care: Soak and remove crusts with warm water and mild soap before applying topical antibiotics
• Mild disease: Mupirocin 2% ointment BID × 5 days [1-2]
• Moderate-severe/multilesional: Cephalexin (children) or dicloxacillin (adults) × 7–10 days [1-2]
• MRSA suspected: Clindamycin, TMP-SMX, or doxycycline (≥8 years) [1-2]
• Ecthyma: Always requires oral antibiotics [2]

Infection control

• Good hand hygiene; wash fomites (towels, linens) [1]
• Keep lesions covered
• Exclude from school/daycare until 12–24 hours after initiating antibiotics or until clinical improvement [1][5]

Outbreak setting: Use systemic (oral) antibiotics to decrease transmission; if poststreptococcal glomerulonephritis outbreak, systemic antibiotics are recommended to eliminate nephritogenic strains [2]

• Discharge (vast majority): Uncomplicated impetigo is managed entirely as an outpatient
• Observation/admission criteria:
  • Extensive bullous impetigo in neonates (concern for SSSS)
  • Signs of systemic toxicity or sepsis
  • Rapidly progressive cellulitis or suspected necrotizing fasciitis
  • Immunocompromised patients with extensive disease
• Specialist consultation:
  • Dermatology: Atypical presentation, treatment failure, recurrent disease
  • Infectious disease: Suspected MRSA, recurrent infections, outbreak management
  • Nephrology: If poststreptococcal glomerulonephritis develops

• Follow-up: Reassess in 3–5 days if no improvement on topical therapy; switch to oral antibiotics if worsening or no response [1]
• Expected course: Lesions typically resolve within 7–10 days with treatment; 2–3 weeks untreated [3]
• Return precautions — advise return if:
  • Lesions spreading despite treatment
  • New fever, increasing redness/swelling, or pain
  • Dark or bloody urine, facial swelling (glomerulonephritis — typically 1–3 weeks post-infection)
  • Joint pain or new rash (rheumatic fever)
• Recurrence prevention: Treat underlying dermatoses (eczema, scabies); consider nasal mupirocin decolonization for recurrent staphylococcal impetigo; maintain good hygiene practices [1]

1. Impetigo: Rapid Evidence Review. — Trang DT, Buck EC, Schoenherr DT. American Family Physician. 2026.

2. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America. — Stevens DL, Bisno AL, Chambers HF, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2014.

3. Impetigo: Diagnosis and Treatment. — Hartman-Adams H, Banvard C, Juckett G. American Family Physician. 2014.

4. Healthy Skin for Children and Young People With Skin of Colour Starts With Clinician Knowledge and Recognition: A Narrative Review. — Ricciardo BM, Kessaris HL, Cherian S, et al. The Lancet. Child & Adolescent Health. 2025.

5. Efficacy and Safety of Ozenoxacin Cream for Treatment of Adult and Pediatric Patients With Impetigo: A Randomized Clinical Trial. — Rosen T, Albareda N, Rosenberg N, et al. JAMA Dermatology. 2018.

6. Interventions for Impetigo. — Koning S, van der Sande R, Verhagen AP, et al. The Cochrane Database of Systematic Reviews. 2012.