How contagious is pneumonia?

Pneumonia, whether caused by viruses or bacteria, is not contagious per se in the sense that it can automatically trigger pneumonia in another person. There are numerous pathogens that can cause pneumonia. In most cases these are bacteria, in some cases viruses and in a few exceptions pneumonia is caused by fungi.

General information on pneumonia can be found under our main topic: PneumoniaViruses are known to pass from one patient to another through the air, i.e. in the form of the so-called droplet infection. The transmission route is therefore relatively simple and happens quickly, especially when people are close to each other. The transmission of bacteria in the case of pneumonia is not so easy, because the bacteria are usually present in the bronchial secretion and do not “fly” freely through the exhaled air.

Fungi, on the other hand, are a rare cause of pneumonia but a form of pneumonia that can also pass quickly from one carrier to another. Fungi that have triggered pneumonia are also present in the exhaled air of the affected patient, usually in the form of small spores. In principle, the fungal spores can also be inhaled by other people through the air, where they can lead to the same course of disease.

In some cases the transmission from animal to human occurs. The pathogen Chlamydia psittaci is found in bird droppings and, if dried droppings are released into the air in summer, it can also be inhaled by humans inadvertently and cause pneumonia. The so-called legionnaire’s disease, caused by legionella, can also be transmitted to humans.

In most cases, the Legionella bacteria are found in the water and pipe systems of older houses. Especially if the base temperature of the water is low, the legionella can survive and multiply for a long time in this system. The name legionnaire’s disease comes from the former legions who were infected with legionella in hotels with old water pipe systems and got pneumonia.

The main infection is the inhalation of the legionellae, which are in evaporating water (water vapour when showering etc.). Besides fungi, chlamydia or legionella, the numerous viruses that cause pneumonia are also transmitted by air. These include influenza viruses, RS viruses and adenoviruses.

Typical bacteria that cause pneumonia are Streptococci, staphylococci, pseudomonads, mycoplasms, E. coli and Klebsiellae. In principle, the pathogens, of whatever kind, which can cause pneumonia are contagious and can be transmitted from person to person via different pathways (but mostly droplet infection through the air). With a few exceptions, however, the pathogens do not necessarily trigger the same symptoms and the same course of disease in the infected patient, i.e.

even if a patient is infected with e.g. streptococci from a fellow patient who has pneumonia, this does not mean that these pathogens also trigger pneumonia in him. Many factors play a role here, which are usually closely related to the immune system. Patients with a suppressed immune system have a comparably higher risk of getting pneumonia.

These are mainly older patients, whose immune system is often less reactive, small children, who do not have a mature immune system and patients, who have many and severe concomitant diseases. The so-called multimorbidity (many diseases running parallel) weaken the immune system and thus increase the probability of infection. Furthermore, pre-treated patients who are pre-treated, e.g. in the case of oncological diseases in the course of chemotherapy, are at high risk of getting pneumonia.

These patients should therefore not stay so close to fellow patients who have pneumonia. Also patients with HIV or patients after organ transplants are immunocompromised and have a high risk of getting pneumonia. Transmission of fungal pneumonia also has an increased risk of being transmitted from person to person, even if there is no immune-reducing previous illness or many accompanying diseases.

Patients who have pneumonia caused by fungi should therefore keep their distance from their environment in the first time. Treated pneumonia, on the other hand, is no longer so infectious.In principle, however, it can be stated that transmission of pneumonia is mainly a problem in patients whose immune system is weakened. In healthy patients, there is in most cases no outbreak of pneumonia, even if the pathogens were inhaled through the air (droplet infection).

The reason is that the immune system in healthy people reacts immediately when pathogens enter the organism. This also happens when pathogens enter the respiratory system (lungs). In the form of macrophages, the pathogens are usually rendered harmless within a very short time and are thus unable to settle in the lungs and multiply. Either the pathogens are degraded by the macrophages or bound and coughed up by means of mucus.