Corynebacterium diphtheriae

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”
  • myocarditis 
• 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)