Diphtheria Frequently Asked Questions

What is diphtheria?
Diphtheria is an acute bacterial disease usually affecting the tonsils, pharynx, larynx and occasionally the skin. The disease is typically caused by the toxin producing bacterium Corynebacterium diphtheriae. Rarely, other Corynebacterium species (C. ulcerans or C. pseudotuberculosis) may produce diphtheria toxin and lead to classic respiratory diphtheria.

What are the signs and symptoms?
Respiratory diphtheria begins 2-5 days after infection with C. diphtheriae. This type of diphtheria typically affects the throat and tonsils. The early symptoms are sore throat, loss of appetite, and slight fever. Within two to three days a bluish-white or grey membrane forms in the throat and on the tonsils (pseudo-membrane) due to the effects of the toxin. This membrane sticks to the soft palate of the throat and may bleed. If there is bleeding, the membrane may become greyish-green or black. The patient may either recover at this point or develop severe weakness and die within six to ten days. Patients with severe diphtheria do not develop a high fever but may develop a swollen neck ("bullneck") and obstructed airway. The toxin produced by the bacteria may also affect other parts of the body including the heart and nervous systems, causing paralysis and cardiac failure. Milder infections resemble streptococcal pharyngitis and the pseudo-membrane may not develop, particularly in vaccinated individuals. The bacteria can also be carried without any symptoms at all.

Nasal diphtheria can be mild and chronic with one sided nasal discharge and superficial ulceration or sores.

Cutaneous diphtheria is usually mild, typically consisting of non-distinctive sores or shallow ulcers and only rarely involving toxic complications. Cutaneous diphtheria is more common in warmer climates and environments of poverty, over crowding and poor hygiene. Cutaneous diphtheria may act as a source of respiratory infection in others.

How serious is the disease?
The disease can be fatal - between 5% and 10% of diphtheria patients die, even if properly treated. If untreated, the disease claims even more lives.

How is diphtheria diagnosed and treated?
For confirmation of diagnosis, health care workers should obtain throat cultures from suspect cases. However, treatment should begin without waiting for culture results.

Anyone who develops diphtheria should be given diphtheria antitoxin and antibiotics. They should be isolated to avoid exposing others to the disease.

Diphtheria antitoxin supplies can be obtained following consultation with the Medical Officer on call, Cherry Orchard Hospital, Dublin (Tel 01 620 6000).

For how long are patients infectious?
Once treated with the appropriate antibiotic, cases typically become non-infectious within 24 hours.

Untreated individuals with diphtheria are usually infectious for 2 to 3 weeks (up to 4 weeks sometimes). Chronic carriers may be infectious for up to 6 months.

Who is affected by diphtheria?
Diphtheria affects people of all ages, but most often it strikes unimmunised children.

In many parts of the world diphtheria continues to be a major public health problem. In 2014, 7,323 diphtheria cases were reported worldwide.

Even among immunised populations immunity decreases with age; approximately 65% of the Irish population over 30 years of age may be susceptible to diphtheria.

Travellers to countries where diphtheria is still common (eastern Europe, India, Southeast Asia, Africa, and South America) are most at risk of disease.

How is diphtheria spread?
Humans are the normal reservoir for Corynebacterium diphtheriae. Cows and farm animals are the most common reservoirs for C. ulcerans, but this strain has also been identified in humans, horses, cats and dogs.

The bacteria are spread by contact with a patient or a carrier. Most typically spread occurs via respiratory droplets from the throat through coughing and sneezing. Occasionally transmission may also occur through contact with articles contaminated with discharges from lesions of infected people and possibly animals. Raw milk has also served as a vehicle for infection. 

Travel, and close contact with cases or carriers, cattle or other farm animals are potential risk factors for infection. Although there is no direct evidence of person-to-person transmission of C. ulcerans infection, there have been incidents that suggest this mode of transmission is possible.


How is diphtheria prevented?
The most effective way of preventing diphtheria is to maintain a high level of immunisation in the community. At least 85% of the population must be immunised to prevent spread of the disease if toxigenic strains are imported from abroad.

Diphtheria immunisation protects by stimulating the production of antitoxin which provides immunity to the effects of the toxin. Diphtheria toxoid is one of the oldest vaccines in current use and was introduced in Ireland in the 1930s.

How many doses of diphtheria vaccine are recommended?
In Ireland, three doses of a vaccine containing diphtheria toxoid (contained in the ‘6 in 1’ vaccine) are given during the first year of life (primary immunization), a booster is given at 4-5 years of age and another booster at 11-14 years of age. Therefore at least 5 doses of vaccine containing diphtheria toxoid are recommended.

Additional boosters may be needed to maintain immunity for those at particular risk of infection. All travellers to epidemic or endemic areas should ensure that they are fully immunised according to the Irish schedule.

All vaccines now used in Ireland to boost protection against tetanus also contain a booster vaccine for diphtheria.

Diphtheria vaccination in laboratory, healthcare workers, veterinarians
Individuals who may be exposed to diphtheria in the course of their work, in microbiology laboratories and clinical infectious disease units, are at risk and must be protected.

Further information on vaccination is available from the HSE National Immunisation Office which provides up-to-date information about HSE immunisation programmes for children, adults and healthcare professionals in Ireland.


How many cases of diphtheria are seen each year in Ireland?
Due to widespread use of diphtheria vaccine since the 1930s the incidence of diphtheria has decreased markedly since the 1940s. In 1948 (first year for which data are available) over 500 diphtheria cases and 30 deaths were reported. The number of cases declined rapidly over the subsequent years and by the 1960s relatively few cases were reported each year. One diphtheria case (C. ulcerans) was notified in Ireland in 2015 and one in 2016. The last diphtheria case (and death) notified prior to this was in 1967.

Last updated: 2018