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BASICS

  • Contagious superficial intraepidermal infection mainly on exposed face and extremities
  • Primary impetigo: infection of normal skin
  • Secondary impetigo: infection on preexisting skin trauma (abrasions, insect bites, eczema)

  • 80% cultures positive for Staphylococcus aureus (alone or with group A Ξ²-hemolytic streptococci)

  • Nonbullous impetigo most common: vesiculopustules rupture β†’ golden crust
  • Bullous impetigo: staphylococcal toxin-mediated large flaccid bullae, common in newborns/young children, <30% cases
  • Folliculitis sometimes considered S. aureus impetigo of hair follicles
  • Ecthyma: deeper ulcerative impetigo often with lymphadenitis

EPIDEMIOLOGY

  • Affects males and females equally
  • Predominant age: children 2 to 5 years
  • Common but no precise prevalence data in the US
  • Poststreptococcal glomerulonephritis possible complication in young children
  • Nursery contamination can cause impetigo neonatorum

ETIOLOGY AND PATHOPHYSIOLOGY

  • S. aureus pure culture 50–90%; more contagious by contact
  • Group A Ξ²-hemolytic streptococci pure culture ~10%
  • Mixed staphylococcal-streptococcal infections common
  • Increasing prevalence of S. aureus, including MRSA strains
  • Transmission by direct contact or insect vectors
  • Lesions develop at trauma or insect bite sites
  • Regional lymphadenopathy may occur

RISK FACTORS

  • Warm, humid climates, tropical/subtropical zones
  • Summer/fall season
  • Minor trauma, insect bites, skin breaches
  • Poor hygiene, poverty, overcrowding
  • Epidemics, wartime conditions
  • Familial spread
  • Underlying conditions: pediculosis, scabies, chickenpox, eczema, contact dermatitis (e.g., Rhus spp.)
  • Contact sports, daycare attendance
  • Colonization by S. aureus or group A Streptococcus

PREVENTION

  • Emphasize family and personal hygiene, especially handwashing
  • Cover wounds promptly
  • Avoid crowding and sharing personal items
  • Treat underlying dermatitis promptly

COMMONLY ASSOCIATED CONDITIONS

  • Malnutrition, anemia
  • Crowded living conditions, poor hygiene
  • Chronic or underlying dermatitis
  • Coinfection with scabies

DIAGNOSIS

History

  • Lesions often painful
  • May have slow or rapid spread
  • Common sites: face around mouth/nose, trauma sites

Physical Exam

  • Early: tender red macules/papules
  • Progression: thin-roofed vesicles/bullae (usually nontender), pustules
  • Weeping shallow ulcers with honey-colored crusts
  • Satellite lesions common
  • Bullae often on buttocks, trunk, face

Differential Diagnosis

Nonbullous

  • Contact dermatitis
  • Chickenpox
  • Herpes simplex
  • Folliculitis
  • Erysipelas
  • Insect bites
  • Severe eczematous dermatitis
  • Scabies
  • Tinea corporis

Bullous

  • Burns
  • Pemphigus vulgaris
  • Bullous pemphigoid
  • Stevens-Johnson syndrome

DIAGNOSTIC TESTS

  • Usually not needed in typical cases
  • Culture pus or bullae fluid if no response to therapy
  • Culture base of lesion after crust removal: grows S. aureus and group A streptococci
  • Streptococcal serologies (ASO titer, anti-DNase B, antihyaluronidase) less reliable, but useful if concerned about poststreptococcal glomerulonephritis
  • Streptozyme test positive for streptococci
  • Consider systemic signs and systemic spread

TREATMENT

General Measures

  • Speeds healing, prevents spread, improves cosmetic outcome
  • Mupirocin ointment TID for minor skin trauma prophylaxis
  • Remove crusts gently, wash 2–3 times daily with antibacterial soap, chlorhexidine, or povidone-iodine
  • Whole-body washing may prevent distant site recurrences

Medication

Topical (limited lesions)

  • Mupirocin 2% ointment TID Γ— 5–7 days (not as effective on scalp)
  • Retapamulin 1% ointment BID Γ— 5 days (costly)
  • Ozenoxacin 1% cream BID Γ— 5 days (costly)

Oral (extensive or bullous)

  • Dicloxacillin (adults 250 mg PO QID; children 12–25 mg/kg/day divided q6h)
  • Cephalexin, cefaclor, cephradine, cefadroxil effective against MSSA
  • For MRSA: clindamycin, tetracyclines, TMP-SMX
  • Duration: 7–10 days

Severe bullous disease

  • IV nafcillin or cefazolin

ISSUES FOR REFERRAL

  • Resistant or extensive infections
  • Immunocompromised patients

ONGOING CARE

  • Restrict athletes from contact sports during active infection
  • Children may return to school 24 hours after starting antimicrobials
  • If no improvement by 7–10 days, culture lesions

PATIENT EDUCATION

  • Handwashing critical to prevent spread, especially in children
  • Avoid sharing personal items

PROGNOSIS

  • Resolution typically within 7–10 days with treatment
  • Antibiotics do not prevent poststreptococcal glomerulonephritis
  • Persistent or recurrent cases: consider S. aureus nasal or perineal carriage; mupirocin nasal ointment BID Γ— 5 days for decolonization

COMPLICATIONS

  • Ecthyma (deeper ulcer)
  • Erysipelas
  • Poststreptococcal glomerulonephritis
  • Cellulitis
  • Bacteremia
  • Osteomyelitis
  • Septic arthritis
  • Pneumonia
  • Lymphadenitis

REFERENCES

  1. Stevens DL, Bisno AL, Chambers HF, et al; Infectious Diseases Society of America. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update. Clin Infect Dis. 2014;59(2):147-159.
  2. Edge R, ArgΓ‘ez C. Topical Antibiotics for Impetigo: A Review of the Clinical Effectiveness and Guidelines. Canadian Agency for Drugs and Technologies in Health; 2017.
  3. Gahlawat G, Tesfaye W, Bushell M, et al. Emerging treatment strategies for impetigo: a systematic review. Clin Ther. 2021;43(6):986-1006.
  4. Del Giudice P, Hubiche P. Community-associated methicillin-resistant Staphylococcus aureus and impetigo. Br J Dermatol. 2010;162(4):905-906.

Clinical Pearls

  • Superficial, intraepidermal infection predominantly caused by Staphylococcus aureus
  • Monitor local resistance patterns to guide antibiotic choice
  • Topical treatment preferred for limited lesions; oral antibiotics reserved for severe or widespread disease
  • Poststreptococcal glomerulonephritis is a rare but serious sequela