Diphtheria (croup) is an infection of the throat by the bacterium Corynebacterium diphteriae.
Diphtheria occurs primarily in temperate climates with high population densities. Today it has become rather rare in our latitudes due to the timely vaccination protection. Since it is still a dangerous infectious disease, children should be immunized against diphtheria from the 3rd month of life.


How can you get infected with diphtheria?

Infection occurs through droplet and smear infection. The germ Corynebacterium diphteriae likes to settle in the human throat and spreads there very quickly.

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The common way of infection is the droplet infection, in which the bacteria reach the throat area via the saliva of an infected person in the area. This can happen from sneezing or coughing in close proximity or while kissing. The less common route of transmission in so-called skin diphtheria is smear infection or infection by contaminated objects, i.e. objects colonized with bacteria. But other entry points via the nose, eyes and skin wounds are also known.

Many people go through a "silent celebration", i.e. they have had contact with the pathogen, but do not get sick. What makes diphtheria unpredictable is the fact that people who have had contact with the germ can still infect others. So you are never sure whether you are infected or not. In tropical and subtropical areas in particular, there is always uncertainty about this if there is insufficient vaccination protection!

incubation period

The incubation period, i.e. the period between infection with the diphtheria bacteria and the onset of the disease in the form of symptoms, is 2-5 days for diphtheria disease.
The bacteria usually get into the throat through a so-called droplet infection. There they nest, multiply and after 2-5 days they trigger the first symptoms, such as severe swelling of the throat, cough and a coating in the throat area.

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Infectivity must be distinguished from the incubation period. This describes the period in which an already infected person is contagious to others. Without treatment for diphtheria, an infected person is contagious to other people around them for between 2 and 4 weeks.

With treatment, the infectivity is only 2 to 4 days.


This is what causes diphtheria Corynebacterium diphtheriae. This belongs to the gram-positive rod bacteria. This means that on the basis of the so-called Gram staining under the microscope, it can be classified into the group of gram-positive bacteria against which e.g. certain antibiotics work particularly well.
The bacterium has a so-called facultative anaerobic growth. In contrast to many other pathogens, it does not depend on air to survive, which is why it can grow even under difficult conditions. This also includes, for example, the fact that it is resistant to the cold, i.e. it survives even at low temperatures.

The bacterium can only trigger diphtheria disease if it has produced the diphtheria toxin. For this to happen, it must be infected by a so-called phage. It's a small virus that specializes in infecting bacteria. If there is a phage in the bacterium, it can produce the diphtheria toxins and release them in the human body when infected.

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The time between infection, i.e. contact with a person infected with diphtheria, and the actual outbreak of symptoms of the disease (incubation period) is only two to four days! Since the germs mainly settle in the throat, a sore throat initially occurs.

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If the patient now looks into the throat, he recognizes a whitish-brown coating (Pseudomembrane, Pharyngeal diphtheria) associated with tonsillar angina (Tonsillitis/Tonsillitis) remind. If you try to remove the plaque with a stick, the lining of the throat will bleed. Difficulty swallowing and a changed voice (aphonic voice) accompany the disease from the beginning.

A typical, sweetish halitosis is perceived by others. The infection rises quickly to deeper neck areas. If the larynx is affected (croup), typical symptoms such as

  • to cough
  • hoarseness
  • Shortness of breath
  • and a choking hazard.

The patients feel seriously ill, have a fever and are in poor general condition.

You might also be interested in: Causes of Sore Throat

Dangers of diphtheria

What are the dangers of infection?

Shortness of breath and the danger of suffocation are the greatest complications of croup. The germ Corynebacterium diphteriae is also able to produce its own poison (diphtheria toxin). This poison can damage numerous organs:

  • Heart muscle inflammation / endocarditis
  • Circulatory shock
  • Kidney failure
  • Neck muscle paralysis and
  • Tongue swelling (Caesar neck)

are just a few of the effects of this poison. If one of the organs has been attacked, there is a mortal danger! Treatment should be given immediately.

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Diphtheria toxin

The bacteria that cause diphtheria are able to produce so-called toxins. When infected with bacteria, these toxic substances are released into the blood of the infected person and can get into the cells of the body via a special mechanism. There they attach to the so-called ribosomes of the cells, which are responsible for the production of proteins. Proteins are an important part of the human body and are needed for cells to survive. The production of proteins in the cell is stopped by the deposition of diphtheria toxins on the ribosomes. This eventually leads to death of the cell (necrosis) after a while, as it cannot survive without these proteins. The death of several cells leads to so-called tissue necrosis, i.e. the death of tissue parts.

The so-called pseudomembranes in the throat, which are typical for diphtheria, consist of the aforementioned dead cells and fibrin, a substance that connects the cells to this skin-like layer in the throat.


How is diphtheria treated?

There are two goals in therapy. On the one hand, the body quickly needs an antidote to the diphtheria toxin; on the other hand, the producer of the poison, i.e. the germ itself, has to be fought in order to counteract a “toxin replenishment”. The antidote (antitoxin, diphtheria-antitoxin-Behring) can be quickly made available by a clinic. Conventional penicillin works against the germ itself.


An antitoxin can be given in therapy against the diphtheria toxin released by the diphtheria bacteria. This drug is very effective in an emergency and neutralizes the diphtheria toxins so that they no longer work and can cause many cells in the body to die.
Since intravenous administration of the antitoxin can occasionally lead to a so-called anaphylactic shock, i.e. a life-threatening excessive immune reaction, this is first injected under the skin and then given intravenously if it is well tolerated.

Vaccination against diphtheria

There are different forms of combination vaccines against diphtheria, for example with tetanus, pertussis and poliomyelitis. These include the common vaccines Boostrix polio® and Repevax®. Other combination forms also include Haemophilus Influenza B and Hepatitis B. A vaccine that prevents diphtheria infection alone is not common in Germany.

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All of these vaccines are so-called dead vaccines, which means that the body is injected with antibodies that work against the bacteria.
As a rule, vaccination is relatively straightforward and has no additional special side effects. However, people with an acute infection with fever and pregnant women should not be vaccinated.

It is important to know that a disease you have suffered does not provide lifelong protection. The body can be attacked again by the bacteria and become sick. Therefore, it is important that all people are vaccinated against diphtheria. Since the vaccination against diphtheria is recommended by the STIKO and is one of the standard vaccinations, diphtheria infections rarely occur in Germany.

Read more about the topic here: Vaccination against diphtheria

When do I have to refresh my vaccination?

The vaccination against diphtheria should be done 4 times in the 1st year of life of every person:

  • in the 2nd, 3rd and 4th month of life
  • between the 11th and 14th month of life

After that, two further vaccinations should be given up to the age of 18:

  • in the 5th-6th age
  • between the ages of 9 and 17

Thereafter, the vaccination should be refreshed every 10 years. However, if there is contact with a person with diphtheria and the vaccination was more than 5 years ago, it is recommended to repeat it immediately.

Can you get diphtheria despite being vaccinated?

The vaccines common today usually offer very good vaccination protection, which is why it is unlikely that you will get diphtheria despite being vaccinated. One should make sure to keep the booster vaccinations regularly. In addition, if there is contact with a potentially infected person and if the period since the last vaccination is more than 5 years, the vaccination should be refreshed immediately.

Consequences of diphtheria

Even if only about five diphtheria cases are known per year in our latitudes, the probability of dying from it or suffering secondary damage is alarmingly high. All parents are therefore advised to have their children vaccinated in good time.


Occasionally, myocarditis can also occur with diphtheria. This occurs in around 20% of all infected people. Myocarditis is an inflammation of the myocardium, the heart muscle. Due to the inflamed muscles, the heart can no longer work as effectively and pump the blood into the body with less force.

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