An Overview of Diphtheria

Learn more about this very rare yet fatal condition

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Diphtheria is a bacterial infection that usually affects the respiratory tract. A characteristic sign of a diphtheria infection is a thick, hard, grayish coating (pseudomembrane) lining the throat. While diphtheria is not common in the developed world due to vaccination, it can cause serious complications, including death, if left untreated.

The widespread use of vaccines has made respiratory diphtheria very rare, especially in developed nations. In 2016, there were only 7,097 cases of diphtheria worldwide reported by the World Health Organization (WHO).

Diphtheria symptoms


Diphtheria used to be a very common cause of disease and death, especially in children. The severity of the infection and diphtheria's symptoms led to its once-macabre nickname—"the strangling angel"—in the decades before the infection was well understood and there was widespread availability of a vaccine.

After someone is exposed to diphtheria bacteria and becomes infected, the respiratory symptoms usually appear within two to five days, though the incubation period may be up to 10 days.

Diphtheria infection can start out similarly to a normal respiratory infection. At first, symptoms may be mild. However, if the infection is not diagnosed and treated, severe complications can develop. The general symptoms of diphtheria include:

  • Fever and chills
  • Sore throat
  • Runny nose
  • Swollen glands in the neck ("bull's neck" appearance)
  • Fatigue and feeling weak
  • Wheezing and difficulty breathing
  • Hoarseness and difficulty talking
  • Racing heart (tachycardia)
  • Nausea and vomiting (more common in children)

One of the hallmark features of diphtheria is the formation of a thick, hard, gray-colored coating (pseudomembrane) lining the throat.

It may coat the tonsils, the nose, and other membranes in the respiratory tract. As the membrane builds up and thickens, it can make it difficult to breathe. It may obstruct the person's airway or make it hard for them to swallow.

When trying to remove or scrape off the membrane, bleeding of the tissue will occur. The membrane is highly infectious and filled with diphtheria toxin. Not only does this mean it can spread the infection, but it can also make the person with diphtheria very ill if the toxin spreads through the body (in a condition known as sepsis).

If the infection spreads to other parts of the body, complications of diphtheria can include:

  • Heart damage or inflammation of the heart (myocarditis)
  • Kidney damage and renal failure
  • Pneumonia or other lung infections
  • Damage to the nerves (neuropathy) which may resolve over time
  • Demyelinating polyneuropathy (inflammatory condition of the nervous system)
  • Paralysis (particularly of the diaphragm)

Another type of diphtheria infection, which is less common, affects the skin. Cutaneous diphtheria is usually less severe than respiratory diphtheria. At first, the skin infections may appear very similar to other chronic conditions like eczema or psoriasis.

Timely and accurate diagnosis is critical, as skin lesions caused by diphtheria bacterium are highly contagious, and the ease with which they shed makes the spread of the disease more likely.

Symptoms of cutaneous diphtheria include:

  • Scaly rash
  • Ulcers
  • Secondary wound infections

Approximately 20% to 40% of people with diphtheria infection of the skin may develop the respiratory infection as well. Diphtheria infection is far more serious when it infects the mucous membranes of the respiratory tract, such as the nose, throat, and lungs.

According to the Centers for Disease Control and Prevention (CDC), even when accurately diagnosed and treatment is started, one in 10 people who contract diphtheria will die from the infection. When the infection goes untreated, the fatality rate for diphtheria is believed to be as high as every one in two people.

People at Higher Risk for Complications

  • Those who haven't received primary vaccination or have missed "booster" shots
  • Those who did not receive a timely diagnosis or for whom treatment was delayed
  • People who have weakened immune systems
  • Anyone under the age of 5 or older than 40 (very young children are especially at risk for complications)

Without treatment, the symptoms usually last for one to two weeks. However, people may experience complications for weeks or even months after contracting diphtheria. If they do not receive treatment, they can also continue to spread the infection to others.


Diphtheria can be caused by one of several strains of bacteria called Corynebacterium diphtheria (C. diphtheria). Most infections of the respiratory tract and skin are caused by strains that release diphtheria toxin, which is then released in the body. Generally speaking, the more toxins that are released, the sicker a person with diphtheria will be. People can also become infected by less common nontoxigenic strains of C. diphtheria, which leads to less-severe symptoms.

Diphtheria infection tends to spread more frequently during the winter and spring.

People who are not vaccinated can catch diphtheria if they are near a person who has it or when traveling to a part of the world where the infection is still common (also called an "endemic" disease).

The bacteria that causes diphtheria is spread when someone inhales droplets from an infected person's cough or sneeze. While less common, the infection can also be spread by touching an infected skin lesion or touching something that has come into contact with secretions from the nose, mouth, or a wound (such as a sick person's bedding, clothes, or an object such as a child's toy).

In most cases, diphtheria is only spread by a person who is feeling sick and showing symptoms. Without treatment, someone who is infected with diphtheria can spread the infection to others for two to six weeks.

It is possible for someone to carry the infection even when they don't feel sick (called an asymptomatic carrier). This is more likely to happen in parts of the world where diphtheria is still common and where most people have not been vaccinated. In most cases, receiving proper treatment for diphtheria infection prevents the spread of the infection and can help reduce the chances of someone becoming a carrier.

Like many infectious diseases, diphtheria is more likely to spread in areas where there is a lack of sanitation, poor hygiene, or where people live together in very crowded spaces and do not have access to vaccines.


If a doctor suspects a person has diphtheria, it's very important they begin treatment as soon as possible, even before the diagnosis is confirmed through tests. In developed nations, the infection is so rare that many doctors will never see a case of it throughout their careers.

Prompt diagnosis and treatment of diphtheria is essential to minimizing the risk of serious complications, including death, as well as preventing the spread of the infection to others.

If a person has symptoms that suggest they have diphtheria, a doctor can take a swab of the person's throat or skin lesion. The culture will be tested in a lab for the bacteria that causes diphtheria as well as the presence of the toxins the bacteria produce.

If there is suspicion a patient has contracted diphtheria, medical professionals must contact the CDC, as they will provide the antitoxin for diptheria.

In the developed world, cutaneous diphtheria is most often seen in people who are homeless or in other situations that make practicing adequate hygiene difficult. In addition, any unvaccinated person can contract diphtheria of any type if they travel to a part of the world where the infection is still common (endemic). This is rare among travelers from Western countries, however, because most are vaccinated.

Men, women, and children of any age and race can get diphtheria, though severe symptoms and complications are more common in children under the age of five.


A person who has been diagnosed with diphtheria may need to be isolated from others while they are sick. Most people who have diphtheria will need to be hospitalized. Depending on the severity of the infection and a person's overall health, they may need to be placed in an intensive care unit. People who are very sick may require a tube in their throat (intubation) to help them breathe. All medical professionals treating patients with suspected or confirmed diphtheria need to take infection-prevention precautions.

Doctors may want to do other tests to see how well a person's immune system is fighting the infection, assess if treatment is working, and help monitor for any potential complications, such as heart or kidney damage. These tests may include:

  • Blood tests to look at white blood cells (leukocytes)
  • EKG to assess the heart
  • Soft tissue ultrasound of the neck to assess swelling
  • Blood tests to measure heart function
  • Kidney function tests
  • Urine tests (urinalysis)
  • Other tests or monitoring depending on a person's symptoms and other health problems

People who live with or have had close contact with someone who has diphtheria will also need to receive antibiotic treatment and be closely monitored. Diphtheria is a "notifiable disease," which means medical professionals will need to collect some information about the patient and the people they have had proximity to and report it to their local city or county health department.

A person being treated for diphtheria will not be released from isolation until doctors are sure they can no longer spread the infection. This requires two negative tests for diphtheria bacteria, which is usually 48 hours after receiving the diphtheria antitoxin and starting antibiotic treatment.

Someone who has been severely ill from diphtheria may have a very long recovery and need to limit their activities to prevent complications. Once a person has recovered from diphtheria, they are required to get the vaccine, as getting sick with diphtheria does not make a person immune to the infection for the rest of her or his life.

A Word From Verywell

Diphtheria is a bacterial infection that can be very serious, but it is extremely preventable through vaccination. It is not very common in developed parts of the world, but a person who has not been vaccinated may contract it if they travel to a region where it is still endemic. The infection usually begins with general symptoms of a respiratory infection, such as a sore throat and fever. However, the development of thick, hard, gray-colored coating (pseudomembrane) lining the throat is characteristic of diphtheria infection. This coating causes further health complications. Prompt diagnosis and proper treatment of diphtheria are important to make sure a person gets better and does not spread the infection to others. If you feel you have symptoms of diphtheria, especially if you've traveled to a region where the infection is endemic, be sure to contact a doctor immediately.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

By Abby Norman
Abby Norman is a freelance science writer and medical editor. She is also the author of "Ask Me About My Uterus: A Quest to Make Doctors Believe in Women's Pain."