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For further information, see CMDT Part 33-07: Diphtheria

Key Features

Essentials of Diagnosis

  • Tenacious gray membrane at portal of entry in pharynx

  • Sore throat, nasal discharge, hoarseness, malaise, fever

  • Myocarditis, neuropathy

  • Culture confirms the diagnosis

General Considerations

  • An acute infection with a toxin-producing strain of Corynebacterium diphtheriae

  • Usually attacks the respiratory tract but may involve any mucous membrane or skin wound

  • The organism is spread primarily by respiratory secretions

  • Exotoxin produced by the organism is responsible for myocarditis and neuropathy

Clinical Findings

Symptoms and Signs

  • Nasal, laryngeal, pharyngeal, and cutaneous forms of diphtheria occur

  • Nasal infection produces few symptoms other than a nasal discharge

  • Laryngeal infection may lead to upper airway and bronchial obstruction

  • In pharyngeal diphtheria, the most common form, a tenacious gray membrane covers the tonsils and pharynx

  • Mild sore throat, fever, and malaise are followed by toxemia and prostration

Differential Diagnosis

  • Streptococcal pharyngitis

  • Infectious mononucleosis

  • Viral pharyngitis, eg, adenovirus, herpes simplex virus

  • Vincent angina

  • Arcanobacterium haemolyticum pharyngitis

  • Oral candidiasis


Laboratory Tests

  • The diagnosis is made clinically but can be confirmed by culture of the organism



  • Susceptible persons exposed to diphtheria should receive a booster dose of diphtheria toxoid plus active immunization if not previously immunized, as well as a course of penicillin or erythromycin


  • Prepared from horse serum

  • Must be given in all cases when diphtheria is suspected

  • For mild early pharyngeal or laryngeal disease, dose of antitoxin is 20,000–40,000 units

  • For moderate nasopharyngeal disease, dose is 40,000–60,000 units

  • For severe, extensive, or late (3 days or more) disease, dose is 80,000–100,000 units


  • Either penicillin, 250 mg four times daily orally, or erythromycin, 500 mg four times daily orally, for 14 days is effective, though erythromycin is slightly more effective in eliminating the carrier state

  • Azithromycin or clarithromycin may be as effective as erythromycin

Therapeutic Procedures

  • Removal of membrane by direct laryngoscopy or bronchoscopy may be necessary to prevent or alleviate airway obstruction



  • The patient should be isolated until three consecutive cultures at the completion of therapy have documented elimination of the organism from the oropharynx


  • Myocarditis and neuropathy are the most common and most serious complications

  • Myocarditis causes cardiac arrhythmias, heart block, and heart failure

  • The neuropathy usually involves the cranial nerves first, producing diplopia, slurred speech, and difficulty in swallowing

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