Diphtheria: For Health Professionals

Diphtheria is a disease caused by a bacterium that affects mucous membranes, primarily those of the upper respiratory tract and the skin. The bacterium is most commonly spread through person-to-person contact. Since the inception of immunization programs in the 1930's, diphtheria is rare in Canada. However it occurs worldwide and is still endemic in many countries. The National Advisory Committee on Immunization (NACI) recommends routine immunization against diphtheria.

Agent of disease

Diphtheria is caused by the toxin-producing strains of the bacterium Corynebacterium diphtheriae.



Spectrum of Clinical Illness

Respiratory diphtheria affects the mucous membrane of the upper respiratory tract. Symptoms include a mild fever, sore throat, difficulty swallowing, malaise and loss of appetite. Sites of infection can include the anterior nose, pharynx/tonsils or the larynx. The most common manifestation that leads to systemic infection is pharyngeal/tonsillar diphtheria. It can progress to acute respiratory distress, upper airway obstruction and asphyxia in young children. An adherent, asymmetrical, greyish-white membrane is visible on the tonsils and oropharynx typically within 2 to 3 days of illness.

Patients with severe disease may develop notable swelling in the neck area giving the characteristic bull neck appearance. Systemic complications such as myocarditis and central nervous system effects (such as muscle paralysis) can occur. This happens if the toxin produced at the site of infection is absorbed into the bloodstream. The case-fatality rate is about 5% to 10%.

Localized infection of the skin (cutaneous diphtheria) may occur. It manifests as various types of lesions which can be indistinguishable from impetigo. Cutaneous diphtheria is rarely associated with systemic complications.

Photos of clinical manifestations of diphtheria

Diphtheria causes a characteristic swollen neck, sometimes referred to as bull neck. Source: Centers for Disease Control and Prevention©

Corynebacterium diphtheriae can affect the skin as well as the respiratory system, manifesting as an open wound. Source: Centers for Disease Control and Prevention©

A 13 year old girl with incomplete immunization. She presented with a fever, severe sore throat, bull neck (Panel A), hoarse voice, and respiratory distress for 8 days. She appeared sick, had tachycardia with normal blood pressure, and had bilateral, yellowish white pharyngeal patches with congestion (Panel B). Source: New England Journal of Medicine (Images in Clinical Medicine). October 17, 2013.


Diphtheria is usually transmitted via the respiratory route through inhalation of respiratory droplets or, rarely, by contact with articles soiled with secretions of infected persons. The incubation period is about 2 to 5 days (range 1 to 10 days).

The infectious period in untreated persons is usually 2 weeks or less and rarely more than 4 weeks. Chronic carriers, which are rare, are asymptomatically colonized with C. diphtheriae on the skin or in the nasopharynx. They may shed organisms for 6 months or more. Proper antibiotic therapy terminates shedding within 48 hours.

Disease Distribution (Global)

Diphtheria occurs worldwide and remains endemic in many countries. The number of diphtheria cases is highest during the colder months in temperate zones. In the tropics, seasonal trends are less distinct. In North America, vaccination has greatly reduced the incidence of diphtheria.

Resurgences in diphtheria have been reported in countries with low immunization coverage. For example, diphtheria was a major problem in countries of the former Soviet Union during the 1990s.Over 150,000 cases and 5,000 deaths were reported between 1990 and 1997.

Risk factors

Inadequately or unimmunized travellers to areas with endemic diphtheria are at higher risk of acquiring disease. A list of countries where diphtheria is endemic is available in Health Information for International Travel Yellow Book.

Prevention & control

Diphtheria can be prevented by immunization.

Immunization of all children with diphtheria (only available in a combination vaccine) is recommended at 2, 4, 6 months of age. This is followed by a booster dose at 18 months of age, 4 to 6 years, at 14–16 years of age and then every 10 years (for example, ages 25, 35, 45 years).

Canadians travelling to countries where diphtheria epidemics are occurring should ensure that their vaccination status is up to date.

For further information about the immunization, please refer to the most recent version of the Canadian Immunization Guide.

Diphtheria antitoxin should be administered when there is clinical suspicion of diphtheria. It is not recommended for close contacts of diphtheria cases, whether immunized or not. Diphtheria antitoxin is available through the local public health authorities on an emergency basis.

Epidemiology of diphtheria in Canada

Diphtheria became nationally notifiable in 1924. That year 9,057 cases were reported, the highest annual number of cases ever recorded in Canada.

The diphtheria vaccine was introduced in 1926. Routine immunization in infancy and childhood has been widely practiced in Canada since 1930. By the mid-1950s, routine immunization had resulted in a remarkable decline in the morbidity and mortality of the disease (see Figure 1). Another steep decline in cases occurred in 1980. This has been attributed, in part, to a change in case definition to exclude carriers from reported cases in all provinces and territories.

A small number of toxigenic strains of diphtheria bacilli continue to be detected each year, although classic diphtheria is rare. Since 1993, a total of 19 cases have been reported with a range of 0 to 4 cases annually (see Figure 1). In this time:

  • approximately 26% of cases were between the ages of 0 to 14 years
  • 74% of cases were over 25 years of age

The last death due to diphtheria in Canada was reported in 2010.

Figure 1. Annual number of reported cases of diphtheria, Canada, 1924 – 2012.

Text Equivalent - Figure 1

The image consists of two line graphs showing the reported number of cases of diphtheria in Canada over time in years. There is one main graph and a smaller graph embedded within the main graph at the top right corner.

In the main graph, the x axis represents time in years between 1924 and 2012 and the y axis represents the number of cases starting with 0 at the bottom to 10000 at the top. The year in which Canada introduced the diphtheria vaccine is depicted with an arrow as 1926. The line represents the number of cases, which start from 9057 cases in 1924. A sharp decline in cases occurs from 9010 cases in 1929 to 2031 cases in 1936. The number of cases increases to over 3000 in 1938 and fluctuates around the 3000 mark until it begins another steady decline in 1945 down to 38 cases by 1959.

The smaller graph inserted within the main graph shows the number of diphtheria cases reported between the years 1955 and 2012. The x axis depicts the time in years, and the y axis the number of reported cases starting from 0 at the bottom to 200 at the top. A steady increase in cases in observed from 23 cases in 1964 to 173 cases in 1974 followed by another sharp decline in cases to less than 10 cases reported each year from 1984 onward. Between 0 and 4 cases were reported each year from 1992 to 2012.

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