Corynebacterium diphtheriae - Diphtheria

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Presence of pseudomembrane; pharyngitis with other organ involvement

Laboratory Testing

Differential Diagnosis

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


  • 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)


  • Non-spore forming, unencapsulated, pleomorphic, gram-positive bacillus
  • Produces exotoxin that causes many of the symptoms
  • Asymptomatic carriage occurs in some patients


  • 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
    • Related to severity of disease – rare in mild disease
    • Usually motor neuropathy
  • 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


  • Vaccination


  • Diphtheria antitoxin
  • Antibiotics
  • Supportive therapy
  • Early ICU support for lower respiratory symptoms
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Streptococcus (Group A) Rapid with Reflex to Culture 0028903
Method: Immunoassay/Culture


Negative rapid test does not rule out presence of group A streptococcus

Corynebacterium diphtheriae Culture 0060360
Method: Culture/Identification


Occasionally patient may have asymptomatic carriage of diphtheria organism


U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Recommended Immunization Schedules for Persons Aged 0 Through 18 Years. United States, 2015. Centers for Disease Control and Prevention. Atlanta, GA [Last Updated Jul 2011; Accessed: Nov 2015]

General References

Khodaei I, Sinha A, Dingle A. Diphtheria: a case report. J Laryngol Otol. 2008; 122(12): 1397-400. PubMed

Mokrousov I. Corynebacterium diphtheriae: genome diversity, population structure and genotyping perspectives. Infect Genet Evol. 2009; 9(1): 1-15. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Medical Reviewers

Last Update: September 2016