Impetigo



Impetigo


Irina Margaritescu, MD, DipRCPath

Bruce R. Smoller, MD









A case of impetigo in a 7-year-old girl demonstrates an erythematous patch with peripheral collarette covered by a hemorrhagic crust.






H&E section shows a subcorneal blister with neutrophils image and sparse inflammatory cell infiltrate in the dermis image in a case of bullous impetigo.


TERMINOLOGY


Synonyms



  • Pyoderma, impetigo contagiosa of Tilbury Fox



ETIOLOGY/PATHOGENESIS


Infectious Agents



  • Staphylococcus aureus (S. aureus)



    • Gram-positive, nonmotile, non-spore-forming, catalase-positive cocci


    • Produce extracellular exfoliative exotoxins (exfoliatin A and B)


  • Streptococcus pyogenes (S. pyogenes)



    • a.k.a. group A β-hemolytic streptococci (GABHS)


    • Gram-positive, nonmotile, chain-forming, non-spore-forming, oxidase- and catalase-negative cocci


Pathogenesis



  • Staphylococcal pyodermas



    • Occur in individuals who are carriers of organism in axillary, inguinal, and perianal areas and in anterior nares


    • Predisposing conditions include atopic dermatitis, diabetes mellitus, dialysis, intravenous drug use, and HIV infection


    • Insect bites, dermatophytoses, herpetic infections, varicella, abrasions, lacerations, and thermal burns also contribute to pathogenesis


  • Group A streptococcal pyodermas



    • Occur following colonization of skin from skin of another individual or from patient’s nasopharynx


  • Nonbullous impetigo



    • Currently, S. aureus is prominent pathogen responsible for nonbullous impetigo



      • Accounts for 50-60% of cases


      • In past, S.aureus and S. pyogenes occurred with equal frequency


    • 20-45% of cases are due to combination of S. aureus and S. pyogenes


    • S. pyogenes is still most common cause in developing countries


  • Bullous impetigo



    • Causative agent is gram-positive, coagulase-positive, group II S. aureus, most often phage type 71


    • S. aureus exotoxins cause loss of cell adhesion in superficial dermis, producing blisters in granular cell layer of epidermis


    • Desmoglein-1 is 1 of target proteins for exotoxin A


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Most common bacterial skin infection and 3rd most common skin disease among children


    • Peak incidence occurs during summer and fall


  • Age



    • Both bullous impetigo and nonbullous impetigo affect all ages but mostly affect children < 6 years old


    • Bullous impetigo is more common than nonbullous impetigo in neonates and infants

Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Impetigo
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