Diphtheria (croup) is an infection of the throat by the bacterium Corynebacterium diphteriae. Diphtheria occurs preferably in temperate climate zones with high population density. Today, it has become rather rare in our latitudes due to timely vaccination protection. Since it is nevertheless a dangerous infectious disease, children should be immunized against diphtheria from the age of 3 months.


Infection occurs by droplet and smear infection. The germ Corynebacterium diphteriae likes to settle in the throat of humans and spreads rapidly. The common way of infection is the droplet infection, where the bacteria reach the throat area via the saliva of an infected person in the environment.

This can happen by sneezing or coughing in the immediate vicinity or when kissing. The rarer transmission route in so-called skin diphtheria is the smear infection or infection through contaminated, i.e. colonized with bacteria, objects. However, other entry points via the nose, eyes and skin wounds are also known.

Many people go through a “quiet celebration”, i.e. they had contact with the pathogen, but do not become ill. What makes diphtheria unpredictable is the fact that people who have had contact with the germ can still infect others. One is therefore never clear whether one is now infected or not. Straight one in tropical and subtropical areas is always present an uncertainty over it, if no sufficient inoculation protection is given!

the incubation period, thus the period between an infection with the Diphtherie bacteria and the outbreak of the illness in the form of symptoms, amounts with the Diphtherie illness 2-5 days. The bacteria usually reach the throat via a so-called droplet infection. There they nestle down, multiply and after 2-5 days trigger the first symptoms, such as a severe swelling of the throat, coughing and a coating in the throat area.

From the incubation period, the infectivity must be separated. This describes the period in which an already infected person is contagious for others. Without treatment for diphtheria, an infected person is infectious for other people in his environment for between 2 and 4 weeks.

With treatment, the infectivity is only 2 to 4 days. The pathogen causing diphtheria is Corynebacterium diphtheriae. This belongs to the gram-positive rod bacteria.

This means that it can be classified under the microscope into the group of Gram-positive bacteria, against which, for example, certain antibiotics are particularly effective. The bacterium has a so-called facultative anaerobic growth. In contrast to many other pathogens, it is not dependent on air to survive, which is why it can grow under difficult conditions.

This includes, for example, the fact that it is resistant to cold, i.e. it survives even at lower temperatures. The bacterium can only cause diphtheria if it has produced the diphtheria toxin. For this to happen, it must be infected by a so-called phage. This is a small virus that is specialized in infecting bacteria. If there is a phage in the bacterium, it can therefore produce the diphtheria toxin and release it in the human body when the infection occurs.