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

Related Tests


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: April 2016