Diphtheria: Causes, symptoms, and treatment

Diphtheria is a contagious disease that usually infects the nose and throat.

The hallmark sign is a sheet of grayish material that covers the back of the throat. It is rare in the Western world, but it can be fatal if left untreated.

Fast facts on diphtheria:

Before the development of treatments and vaccines, diphtheria was widespread and mostly affected children under the age of 15.

Some of the symptoms of diphtheria are similar to those of the common cold.

Complications include nerve damage, heart failure and, in some cases, death.

Diagnosis is confirmed by swab specimens and laboratory testing.

Treatment is with antitoxin and antibiotics while the patient is isolated and monitored in intensive care.

What is diphtheria?

Doctor checking patient for swollen lymph node glands.
A ‘bull neck’ is a common symptom of diphtheria.

Diphtheria is a highly contagious bacterial infection of the nose and throat. Thanks to routine immunization, diphtheria is a disease of the past in most parts of the world. There have only been five cases of the bacterial infection in the United States in the last 10 years.

In countries where there is a lower uptake of booster vaccines, however, such as in India, there remain thousands of cases each year. In 2014, there were 7,321 cases of diphtheria reported to the World Health Organization (WHO), globally.

In people who are not vaccinated against the bacteria that cause diphtheria, infection can cause serious complications, such as nerve problems, heart failure, and even death.

Overall, 5 to 10 percent of people who get infected with diphtheria will die. Some people are more vulnerable than others, with a mortality rate of up to 20 percent in infected people under 5 year or older than 40 years of age.


Diphtheria is an infectious disease caused by the bacterial microorganism known as Corynebacterium diphtheriae. Other Corynebacterium species can be responsible, but this is rare.

Some strains of this bacterium produce a toxin, and it is this toxin that causes the most serious complications of diphtheria. The bacteria produce a toxin because they themselves are infected by a certain type of virus called a phage.

The toxin that is released:

inhibits the production of proteins by cells

destroys the tissue at the site of the infection

leads to membrane formation

gets taken up into the bloodstream and distributed around the body’s tissues

causes inflammation of the heart and nerve damage

can cause low platelet counts, or thrombocytopenia, and produce protein in the urine in a condition called proteinuria

How do you catch diphtheria?

Diphtheria is an infection spread only among humans. It is contagious by direct physical contact with:

droplets breathed out into the air

secretions from the nose and throat, such as mucus and saliva

infected skin lesions

objects, such as bedding or clothes an infected person has used, in rare cases

The infection can spread from an infected patient to any mucous membrane in a new person, but the toxic infection most often attacks the lining of the nose and throat.

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Specific signs and symptoms of diphtheria depend on the particular strain of bacteria involved, and the site of the body affected.

One type of diphtheria, more common in the tropics, causes skin ulcers rather than respiratory infection.

These cases are usually less serious than the classic cases that can lead to severe illness and sometimes death.

The classic case of diphtheria is an upper respiratory infection caused by bacteria. It produces a gray pseudomembrane, or a covering that looks like a membrane, over the lining of the nose and throat, around the area of the tonsils. This pseudomembrane may also be greenish or blueish, and even black if there has been bleeding.

Early features of the infection, before the pseudomembrane appears, include:

low fever, malaise, and weakness.

swollen glands on the neck

Swelling of soft tissue in the neck, giving a ‘bull neck’ appearance

nasal discharge

fast heart rate

Children with a diphtheria infection in a cavity behind the nose and mouth are more likely to have the following early features:

nausea and vomiting

chills, headache, and fever

After a person is first infected with the bacteria, there is an average incubation period of 5 days before early signs and symptoms appear.

After the initial symptoms have appeared, within 12 to 24 hours, a pseudomembrane will begin to form if the bacteria are toxic, leading to:

a sore throat.

difficulty swallowing

possible obstruction that causes breathing difficulties

If the membrane extends to the larynx, hoarseness and a barking cough are more likely, as is the danger of complete obstruction of the airway. The membrane may also extend further down the respiratory system toward the lungs.


Potentially life-threatening complications can occur if the toxin enters the bloodstream and damages other vital tissues.

Myocarditis, or heart damage

Myocarditis is an inflammation of the heart muscle. It can lead to heart failure, and the greater the degree of bacterial infection, the higher the toxicity to the heart.

Myocarditis might cause abnormalities that are only apparent on a heart monitor, but it has the potential to cause sudden death.

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