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.

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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.

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.

Heart problems usually appear 10 to 14 days after the start of the infection, although problems can take weeks to appear. Heart problems associated with diphtheria include:

  • changes visible on an electrocardiograph (ECG) monitor.
  • atrioventricular dissociation, in which the chambers of the heart stop beating together
  • complete heart block, where no electrical pulses travel across the heart.
  • ventricular arrhythmias, which involve the beating of the lower chambers becoming abnormal
  • heart failure, in which the heart is unable to maintain sufficient blood pressure and circulation

Neuritis, or nerve damage

Neuritis is inflammation of nerve tissue that results in damage to nerves. This complication is relatively uncommon and usually appears after a severe respiratory infection with diphtheria. Typically, the condition develops as follows:

  1. In the 3rd week of illness, there can be paralysis of the soft palate.
  2. After the 5th week, paralysis of eye muscles, limbs, and diaphragm.
  3. Pneumonia and respiratory failure may occur due to paralysis of the diaphragm.

Less severe disease from infection at other locations

If the bacterial infection affects tissues other than the throat and respiratory system, such as the skin, the illness is generally milder. This is because the body absorbs lower amounts of the toxin, especially if the infection only affects the skin.

The infection can coexist with other infections and skin conditions and may look no different from eczema, psoriasis, or impetigo. However, diphtheria in the skin can produce ulcers where there is no skin at the center with clear edges and sometimes grayish membranes.

Other mucous membranes can become infected by diphtheria – including the conjunctiva of the eyes, women’s genital tissue, and the external ear canal.

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A diagnosis of diphtheria may be made by analyzing tissue samples under a microscope.

There are definitive tests for diagnosing a case of diphtheria, so if symptoms and history cause a suspicion of the infection, it is relatively straightforward to confirm the diagnosis.

Doctors should be suspicious when they see the characteristic membrane, or patients have unexplained pharyngitis, swollen lymph nodes in the neck, and low-grade fever.

Hoarseness, paralysis of the palate, or stridor (high-pitched breathing sound) are also clues.

Tissue samples taken from a patient with suspected diphtheria can be used to isolate the bacteria, which are then cultured for identification and tested for toxicity:

  • Clinical specimens are taken from the nose and throat.
  • All suspected cases and their close contacts are tested.
  • If possible, swabs are also taken from under the pseudomembrane or removed from the membrane itself.

The tests may not be readily available, and so doctors may need to rely on a specialist laboratory.

Treatment is most effective when given early, so a quick diagnosis is important. The antitoxin that is used cannot fight the diphtheria toxin once it has bound with the tissues and caused the damage.

Treatment aimed at countering the bacterial effects has two components:

  • Antitoxin – also known as anti-diphtheritic serum – to neutralize the toxin released by the bacteria.
  • Antibiotics – erythromycin or penicillin to eradicate the bacteria and stop it from spreading.

Patients with respiratory diphtheria and symptoms would be treated in an intensive care unit in the hospital, and closely monitored. Healthcare staff may isolate the patient to prevent the spread of the infection.

This will be continued until tests for bacteria repeatedly return negative results in the days following the completion of the course of antibiotics.

Humans have known about diphtheria for thousands of years. Its timeline is as follows:

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Nowadays, diphtheria is extremely rare thanks to widespread vaccination against the infectious disease.
  • 5th century BCE: Hippocrates is first to describe the disease. He observes that it can cause the formation of a new layer on mucous membranes.
  • 6th century: First observations of diphtheria epidemics by the Greek physician Aetius.
  • Late 19th century: The bacteria responsible for diphtheria are identified by the German scientists Edwin Klebs and Friedrich Löffler.
  • 1892: Antitoxin treatment, derived from horses, first used in the U.S.
  • 1920s: Development of the toxoid used in vaccines.

Vaccines are routinely used to prevent diphtheria infection in almost all countries. The vaccines are derived from a purified toxin that has been removed from a strain of the bacterium.

Two strengths of diphtheria toxoid are used in routine diphtheria vaccines:

  • D: a higher-dose primary vaccine for children under 10. This is usually given in three doses – at 2, 3, and 4 months of age.
  • d: a lower-dose version for use as a primary vaccine in children over 10, and as a booster for reinforcing the usual immunization in babies, about 3 years after the primary vaccine, normally between 3.5 and 5 years of age.

Modern vaccination schedules include diphtheria toxoid in the childhood immunization, known as diphtheria and tetanus toxoids and acellular pertussis vaccine (DTaP).

This vaccine is the option of choice recommended by the U.S. Centers for Disease Control and Prevention (CDC), and more information is provided, including why some children should not get the DTaP vaccine or should wait.

The doses are given the following ages:

  • 2 months
  • 4 months and after an interval of 4 weeks
  • 6 months and after an interval of 4 weeks
  • 15 to 18 months and after an interval of 6 months

If the fourth dose is given before the age of 4, this fifth, booster dose is recommended at 4 through 6 years of age. However, this is not needed if the fourth primary dose was given on or after the fourth birthday.

    Booster doses of the adult form of the vaccine, tetanus-diphtheria toxoids vaccine (Td), may be needed every 10 years to maintain immunity.