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impetigo

Superficial infection involving the epidermis characterized by crusted erosions or ulcerations. Etiology: 1) Staphylococcus aureus a) most commonly phage group 2, type 71 b) etiologic agent of Staphylococcal scalded skin syndrome same 2) Streptococcus pyogenes 3) primary infection of superficial break in skin 4) secondary infection of pre-exsiting dermatosis 5) predisposing factors a) colonization of skin by S aureus & S pyogenes b) warm ambient temperature c) high humidity d) dermatosis (esp atopic dermatitis) 6) precipitating factors - insect bite [2] Epidemiology: 1) primary infections more common in children - most common bacterial infection in chidren [10] 2) secondary infections occur at any age 3) common disorder, very contagious [3] 4) 25% of patients are nasal carriers of S aureus 5) acquired by person to person contact [2] Pathology: 1) vesicle formation in subcorneal or granular layer 2) acantholysis 3) spongiosis 4) perivascular infiltrate of neutrophils & lymphocytes in dermis 5) gram positive cocci within neutrophils in vesicles 6) elaboration of S aureus exotoxin (exfoliatin) [2] - same toxin causes Staphylococcal scalded skin syndrome Clinical manifestations: 1) durations of lesions: days to weeks 2) variable pruritus 3) non-bullous: small vesicles or pustules rupture resulting in erosions which become crusted 4) bullous: a) vesicles or bullae rupture & decompress b) with unroofing, erosions form c) indicates infection with Staphylococcus 5) crusts may be gold (honey-colored) to hemorrhagic 6) lesions round or oval, 1-3 cm in size 7) scattered, discrete lesions, may be larger confluent lesions 8) satellite lesions occur by auto-inoculation 9) itchy, raised, weeping patches with scaly borders that develop honey-colored crusts 10) distribution: a) face, arms, legs, buttocks b) bullous: trunk, face, hands, intertriginous sites 11) regional lymphadenopathy may be present * images [4,5,10] Laboratory: 1) Gram stain of lesion - Gm+ cocci in chains & clusters within neutrophils 2) wound culture 3) complete blood count (CBC): +/- leukocytosis 4) serology: anti-DNAse beta indicates prior group A Streptococcal infection 5) biopsy Differential diagnosis: 1) non-bullous impetigo - excoriation - perioral dermatitis - seborrheic dermatitis - contact dermatitis - Herpes simplex - Dermatophytosis 2) bullous impetigo - contact dermatitis - Herpes simplex - Herpes gladiatorum, wrestlers - clusters of clear fluid-filled vesicles (clustered papules) with surrounding erythema that crust over - Herpes zoster - folliculitis - burns - bullous pemphigoid - dermatitis herpetiformis 3) erysipelas (group A streptococcus) Complications: 1) also see ecthyma 2) non suppurative complications of group A streptococci Management: 1) topical agents a) may be sufficient for limited disease of head & neck b) topical antibiotic after soaking of crusts - mupirocin (Bactroban) TID to affected skin & to nares for 7-10 days - bacitracin [11] c) benzoyl peroxide (prevention) 2) systemic antibiotics for more extensive disease a) Staphylococcus aureus - dicloxacillin 250-500 mg PO QID - cephalexin - 250-500 mg PO QID for 10 days (adults) - 40-50 mg/kg/day for 10 days (children) - amoxicillin clavulanate (Augmentin) - 20 mg/kg/day divided TID for 10 days - macrolides for penicillin-sensitive individuals - erythromycin - 1-2 g/day divided QID for 10 days (adults) - 40 mg/kg/day divided QID for 10 days (children) - clarithromycin 250-500 mg PO BID for 10 days - azithromycin 250 mg QD for 5-7 days - clindamycin - 150-300 mg QID for 10 days (adults) - 15 mg/kg/day divided QID for 10 days (children) b) methicillin-resistant Staphylococcus aureus (MRSA) - mupirocin ointment - minocycline 100 mg PO BID for 10 days - doxycycline 100 mg PO BID - Bactrim DS 1-2 tabs QD - ciprofloxacin 500 mg PO BID c) group A streptococcus (S pyogenes) - penicillin VK 250 mg PO TID - benzathine penicillin - 600,000 units IM (< 6 years of age) - 1,200,000 units IM (> 6 years of age) - erythromycin 250-500 mg PO QID for 10 days - cephalexin 250-500 mg QID for 10 days 3) prognosis - untreated lesions progress for several weeks & with poor hygiene may form ecthyma - most cases resolve spontaneously - very contagious 4) prevention - reoccurence may occur because of failure to erradicate infection or reinfection from family member - mupirocin to nares of patient & family members for 5 days - benzoyl peroxide soap

Related

cellulitis erysipelas Staphylococcal scalded skin syndrome

General

bacterial infection skin infection vesiculobullous dermatitis

References

  1. Color Atlas & Synopsis of Clinical Dermatology, Common & Serious Diseases, 3rd ed, Fitzpatrick et al, McGraw Hill, NY, 1997, pg 604-609
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 15, 16, 17, 18. American College of Physicians, Philadelphia 1998, 2009, 2012, 2017, 2018.
  3. Geriatrics at your Fingertips, 13th edition, 2011 Reuben DB et al (eds) American Geriatric Society
  4. Lewis LS, Steele RW (images) Medscape: Impetigo http://emedicine.medscape.com/article/965254-overview
  5. DermNet NZ. Impetigo (images) http://www.dermnetnz.org/bacterial/impetigo.html
  6. Hartman-Adams H, Banvard C, Juckett G. Impetigo: diagnosis and treatment. Am Fam Physician. 2014 Aug 15;90(4):229-35. Review. PMID: 25250996 Free Article
  7. NEJM Knowledge+ Question of the Week. May 21, 2019 https://knowledgeplus.nejm.org/question-of-week/1657/
  8. Koning S, van der Sande R, Verhagen AP et al Interventions for impetigo. Cochrane Database Syst Rev. 2012 Jan 18;1:CD003261. Review. PMID: 22258953
  9. Hartman-Adams H, Banvard C, Juckett G. Impetigo: diagnosis and treatment. Am Fam Physician. 2014 Aug 15;90(4):229-35. Review. PMID: 25250996 Free Article
  10. Elkston CA, Elkston DM Bacterial Skin Infections: More Than Skin Deep. Medscape. July 19, 2021 https://reference.medscape.com/slideshow/infect-skin-6003449
  11. Kosar L, Laubscher T. Management of impetigo and cellulitis: simple considerations for promoting appropriate antibiotic use in skin infections. Can Fam Physician. 2017;63:615-8. PMID: 28807958