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Updated: Jun 1 2018

Corynebacterium diphtheriae

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  • Snapshot
    • A 4-year-old girl presents to the emergency room for a fever and sore throat. She recently visited Thailand for 2 months with her parents and had just flown back a couple of days ago. Her parents report that she has not had any of her recommended immunizations, as they have traveled all over the world. On physical exam, there is a grayish-white membrane covering her soft palate. When irritated by a tongue depressor, the membrane oozes with blood. She also has marked cervical lymphadenopathy and edema of the neck. She is immediately admitted for monitoring, antibiotics, and antitoxin.
  • Introduction
    • Classification
      • Corynebacterium diphtheriae
        • aerobic gram-positive rod
        • produces diphtheria toxin
      • transmission
        • respiratory droplets
    • Epidemiology
      • demographics
        • rare in the US
        • more common in developing countries
    • Pathogenesis
      • diphtheria exotoxin inactivates elongation factor (EF-2) via ADP-ribosylation
        • inhibits protein synthesis, causing necrosis in respiratory, cardiac and central nervous system tissue
        • affects mucous membranes, especially the respiratory tract
      • exotoxin is encoded by β-prophage
    • Associated conditions
      • diphtheria
      • cutaneous diphtheria
        • ulcerative lesions or cellulitis can occur independently of respiratory diphtheria
    • Prevention
      • DTap vaccine
        • vaccine against diphtheria, tetanus, and pertussis
        • 5 doses before school-age, completed by 4-6 years of age
      • Tdap vaccine
        • booster vaccine at 11-12 years of age
        • should also be given to pregnant mothers and those around them
      • Td vaccine
        • tetanus and diphtheria toxoid vaccine at 10-year intervals
    • Prognosis
      • symptoms are insidious
      • mortality is higher in young children, but generally good with prompt treatment
  • Presentation
    • Symptoms
      • fever
      • sore throat
      • malaise
      • may have a croup-like cough
    • Physical exam
      • pseudomembranous pharyngitis
        • gray or bluish white membrane seen on soft palate, tonsils, or back of the throat
        • bleeds easily if irritated
        • develops 2-3 days after symptoms
      • severe cervical lymphadenopathy
        • “bull neck”
      • arrhythmias
  • Studies
    • Bacterial culture
      • gram-positive rods with blue and red granules (metachromically) seen on culture
        • cysteine-tellurite agar (appears as black colonies)
        • Löffler medium
      • positive Elek test for diphtheria toxin
    • Making the diagnosis
      • most cases are clinically diagnosed and confirmed with a culture
  • Differential
    • Streptococcal pharyngitis
      • distinguishing factor
        • no pseudomembrane on mucous membranes
  • Treatment
    • Medical
      • diphtheria antitoxin
        • indication
          • all patients
      • antibiotics
        • indications
          • all patients
        • drugs
          • erythromycin
          • penicillin G
  • Complications
    • Airway compromise from soft tissue swelling
    • Heart failure from myocarditis
    • Secondary bacterial infection (e.g., pneumonia)
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