Corynebacterium diphtheriae - Diphtheria

Classic diphtheria is characterized by the formation of a pseudomembrane on respiratory mucous membranes. Initial testing includes CBC and a rapid strep test. A diphtheria culture is usually diagnostic if disease symptoms are present.

Diagnosis

Indications for Testing

  • Presence of pseudomembrane
  • Pharyngitis with other organ involvement

Laboratory Testing

Differential Diagnosis

Background

Epidemiology

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

Organism

  • Gram-positive bacillus
    • Not 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 involvement
    • 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

Prevention

Vaccination

ARUP Lab Tests

Identify Corynebacterium diphtheriae in clinical specimens

Related Tests

Identify infectious process

Rule out more common cause of pharyngitis

If Streptococcus (Group A) rapid test is negative and patient is ≤18 years, culture will be added for confirmation

Evaluate the ability of a patient to produce antibody to pure protein vaccines after vaccination to rule out antibody deficiency

Evaluate the ability of a patient to produce antibody to pure protein vaccine after vaccination to rule out antibody deficiency

Evaluate the ability of a patient to produce antibody to pure protein vaccines (diphtheria and tetanus) and protein conjugated bacterial (Haemophilus influenza) vaccines after vaccination to rule out antibody deficiency

Medical Experts

Contributor

Fisher

Mark A. Fisher, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Bacteriology, Special Microbiology, and Antimicrobial Susceptibility Testing, ARUP Laboratories

References

Additional Resources