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Reporting Obligations

Confirmed and suspected cases shall be reported immediately by telephone to the local Health Unit.

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Aetiologic Agent

Diphtheria is caused by Corynebacterium diphtheria, an aerobic Gram-positive bacillus with four biotypes: gravis, mitis, belfanti and intermedius. Strains may be toxigenic or nontoxigenic. Only the toxigenic strains produce exotoxin and can cause serious diseases. The nontoxigenic strains produce a milder symptomatic clinical illness and have been associated with infective endocarditis. Whether a strain is toxigenic is assessed by the presence of the tox gene and confirmation of toxin using the Elek test.

Clinical Presentation

Acute bacterial disease primarily involving the pharynx, tonsils, larynx, nose, occasionally other mucous membranes or skin and sometimes conjunctivae or vagina.

Diphtheria may appear as mild or chronic unilateral mucopurulent to serosanguinous nasal discharge and excoriations. Onset of symptoms often cannot be distinguished from those of a common cold.

Pharyngeal and tonsillar diphtheria initially presents with low-grade fever, sore throat, difficulty swallowing, malaise and anorexia. The characteristic lesion is an asymmetrical adherent greyish white membrane with surrounding inflammation visible on the tonsils and oropharynx within two to three days of illness. Neck swelling and enlarged cervical lymph nodes may give the appearance of a “bull neck”. Pharyngeal membranes may extend into the trachea resulting in upper airway obstruction and subsequent acute respiratory distress; asphyxia can occur in young children. Systemic complications from dissemination of diphtheria toxin can result in myocarditis and central nervous system effects.

Laryngeal diphtheria can be confined to this site or an extension of pharyngeal diphtheria, characterized by fever, hoarseness, stridor and a barking cough that can progress to airway obstruction, coma and death.

Modes of Transmission

Transmission is most often person-to-person spread from the respiratory tract. Both cases and carriers can be a source of infection. Rarely, transmission may occur from skin lesions or articles soiled with discharges from lesions of infected persons (fomites).

Incubation Period

Usually 2–5 days but can range from 1–10 days.

Period of Communicability

Variable; until virulent bacilli have disappeared from discharges and lesions, usually two weeks or less and seldom more than four weeks for respiratory diphtheria. Chronic carriers may shed organisms for six months or more. Effective antibiotic therapy promptly terminates shedding.

Risk Factors/Susceptibility


Recent travel to an area with endemic diphtheria.

Crowded environments.

Poor hygiene.

Diagnosis and Laboratory Testing

Notify your local public health laboratory prior to submitting a specimen for testing. Specify “diphtheria culture” on the requisition.

Diphtheria is diagnosed based on the isolation of toxigenic Corynebacterium diphtheria from throat, nose, cutaneous sites, exudate of membrane, or isolation of other toxigenic Corynebacterium species from one of these sites. Swabs should be taken for culture before antibiotic therapy is initiated. A comprehensive case history should be obtained to support the diagnosis, including onset, symptoms, immunization status, and travel history within the last two weeks.

After the C. diphtheria organism is isolated, the Elek test will be done to identify if it is a toxigenic strain. A toxic gene PCR result should be acted upon for public health management, without waiting for confirmation of the Elek test.

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Treatment and Case Management

Medical treatment should be provided immediately without waiting for laboratory confirmation. Anti-toxin should be administered as soon as possible to be effective.

Diphtheria antitoxin can be accessed through the ministry during business hours by calling 416-327-7392. After-hours and on weekends and holidays please call the ministry’s Health Care Provider Hotline at 1-866-212-2272.

Refer to the most current version of the ministry’s document Diphtheria Guide for Healthcare Professionals.

Antibiotic treatment should be provided to eliminate the organism and to prevent transmission. It is not a substitute for antitoxin. Cases should be treated with appropriate antibiotics, intramuscular procaine penicillin G or parenteral erythromycin until oral antibiotics can be safely swallowed, in accordance with treatment guidelines provided by the Public Health Agency of Canada or other expert body.

Active immunization against diphtheria should be undertaken during convalescence from diphtheria as disease does not necessarily confer immunity.

Contact management will need to be discussed with your local Public Health Unit. Risk of infection is directly related to duration of contact, the type of contact and intensity of exposure.

Patient Information

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Additional Resources

Ministry of Health and Long-Term Care. “Diphtheria Guide for Health Care Professionals”, April 2018.

Publicly Funded Immunization Schedule for Ontario, January 2021.


Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2022.