Corynebacterium diphtheriae - Diphtheria

Classic diphtheria is characterized by the formation of a pseudomembrane on respiratory mucous membranes.

Epidemiology

• Incidence – very rare in U.S. due to vaccination
• Age – usually children <15 years who are unvaccinated or incompletely vaccinated
• Transmission – airborne or direct contact (respiratory secretions or skin lesion)

Organism

• Gram-positive bacillus
  • Non-spore forming
  • Unencapsulated
  • Pleomorphic
• Produces exotoxin that causes many of the symptoms
• Results in asymptomatic carriage in some patients

Pathophysiology

• Virulence is mediated by prophage-encoded exotoxin
• Toxin induces dense necrotic coagulum on mucous membranes
  • Causes underlying soft-tissue edema

Clinical Presentation

• Incubation period – 2-4 days
• Respiratory tract
  • Anterior nasal disease
  • Faucial disease – classic membranes on pharynx and tonsils, cervical adenopathy and fever
  • Laryngeal and tracheobronchial disease – hoarseness, dyspnea, stridor, and brassy cough
• Cardiac disease – myocarditis
  • Mortality 3-4 times that of patients without cardiac involvement
  • Related to toxin release
• Neurologic disease – demyelinating neuropathy
  • Usually motor neuropathy
  • Related to severity of disease – rare in mild disease
• Renal disease – proteinuria, renal failure
• Cutaneous disease – chronic nonhealing ulcers with dirty gray membrane, often in mixed infections with Staphylococcus aureus and group A streptococci
• Invasive disease
  • Endocarditis
  • Mycotic aneurysms
  • Osteomyelitis
  • Septic arthritis

Prevention

• Vaccination