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Clinical Summary

Diphtheria is a rare but highly contagious disease caused by the exotoxin-producing bacterium C diphtheriae. It is transmitted either by direct contact or through respiratory aerosolization. Many adults are now susceptible to diphtheria because their vaccine-induced immunity decreased over time or owing to decreased opportunity for naturally acquired immunity.

Diphtheria may involve any mucous membrane, but most commonly it affects the mucosa of the upper respiratory tract. It typically produces an ulcerated pharyngeal mucosa with a white-to-gray inflammatory pseudomembrane, classically with a “wet mouse” odor. Patients present with symptoms, in order of frequency, of fever, sore throat, weakness, pain with swallowing, change in voice, loss of appetite, neck swelling, difficulty breathing, and nasal discharge.

While the organism remains localized to the mucosa, hematogenous spread of the exotoxin typically produces myocarditis or peripheral neuropathies. Case fatality rates from diphtheria range from 5% to 20% and are due to either tracheobronchial obstruction by the pseudomembrane acutely or cardiac complications several weeks after the primary infection.

Management and Disposition

The diagnosis is initially made clinically and confirmed by successful isolation and toxigenicity testing of C diphtheriae.

Antitoxin, available from the Centers for Disease Control and Prevention (CDC), is the mainstay of therapy and must be given even before laboratory confirmation. Erythromycin or penicillin given promptly when diphtheria is suspected has been shown to decrease both exotoxin production and spread of the bacterium.

Patients require hospital admission for observation of airway obstruction, pulmonary support, and intravenous hydration and antibiotics. Strict isolation is essential.


  1. Outcome is improved with early treatment; thus, the diagnosis of diphtheria must be made clinically and treatment begun empirically before bacteriologic confirmation.

  2. Patients with a membranous pharyngitis need to be questioned regarding immunization, exposures, and recent travel.

  3. All contacts should have a booster dose of vaccine (TD or Td, depending on age), while nonimmune contacts should also be given prophylactic antibiotics after a throat swab.


Diphtheria Pharyngitis. An exudative pharyngitis with a gray pseudomembrane is seen in this patient with diphtheria. (Photo contributors: Dileep C. Unnikrishnan, MD, and Nadeem Kocheri, MD.)

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