Which germs can cause pneumonia?

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Pneumonia is usually caused by . The specific that cause it depend, among other things, on where you pick up the . Pneumonia is rarely a viral or fungal . But even then, other are usually involved, too.

When the air sacs () and the surrounding lung tissue become infected, bacterial pathogens are usually responsible. Other causes such as the inhalation of toxic substances or allergic reactions are comparatively rare.

How do germs get into our lungs?

The and other germs enter the lungs when tiny saliva or water droplets are inhaled (droplet ). But people sometimes also become ill because they swallowed the wrong way. That means that germs from the mouth and throat, food residue or stomach content can enter the airways and lead to . The medical term for this is aspiration . Only rarely do the germs spread from another infected part of the body to the lungs via the blood.

Which bacteria are responsible?

Bacterial is most frequently caused by called pneumococci. Other types of such as haemophilus influenzae or mycoplasma pneumoniae sometimes also cause the disease.

People who develop in a hospital or nursing home rather than at home are at greater risk of other causing the . They include staphylococci, enterobacteria such as klebsiellae or escherichia coli (E. coli), or the “hospital bug” pseudomonas aeruginosa. These types of germs can lead to complications because they are often more difficult to treat.

Can it be caused by viruses?

Pneumonia rarely develops without being involved. If that happens, viruses might then be the cause, especially viruses that can lead to infections of the airways such as influenza or special viruses called RS (respiratory syncytial) viruses. But measles and coronaviruses can also cause . The SARS-CoV-2 pathogen is one such coronavirus. It can cause COVID-19, which infects the lungs.

Do fungal infections also play a role?

Pneumonia can also be caused by a fungal , for instance by yeast and molds, or the pneumocystis jirovecii sac fungus. But that is rare. Fungal infections of the lungs generally only develop in people with severely weakened immune systems, for instance as a result of AIDS.

Why are bacteria still important even if there are other causes?

Bacteria can spread more easily if the airways are already infected by viruses. Doctors call that a bacterial superinfection or bacterial secondary . A superinfection can lead to bacterial , or make viral worse. That is why people who already have viral are generally given . They are used to prevent an additional bacterial rather than actually fight the viruses.

Deutsche Gesellschaft für Pädiatrische Infektiologie (DGPI), Gesellschaft für Pädiatrische Pneumologie (GPP). Management der ambulant erworbenen Pneumonie bei Kindern und Jugendlichen (pädiatrische ambulant erworbene Pneumonie, pCAP) (S2k-Leitlinie, in Überarbeitung). AWMF-Registernr.: 048-013. 2017.

Deutsche Gesellschaft für Pneumologie und Beatmungsmedizin (DGP). S3-Leitlinie: Behandlung von erwachsenen Patienten mit ambulant erworbener Pneumonie – Update 2021. AWMF-Registernr.: 020-020. 2021.

Herold G. Innere Medizin. Köln: Selbstverlag; 2017.

Kasper DL, Fauci AS, Hauser SL, Longo DL, Jameson JL, Loscalzo J. Harrison's Principles of Internal Medicine. New York: McGraw-Hill; 2015.

Lux LJ, Posey RE, Daniels LS, Henke DC, Durham C, Jonas DE et al. Pharmacokinetic/Pharmacodynamic Measures for Guiding Antibiotic Treatment for Hospital-Acquired Pneumonia. 11.2014. (AHRQ Comparative Effectiveness Reviews; Volume 136).

National Institute for Health and Care Excellence (NICE). Pneumonia: Diagnosis and management of community- and hospital-acquired pneumonia in adults. 03.12.2014. (NICE Clinical Guidelines; Volume 191).

Prina E, Ranzani OT, Torres A. Community-acquired pneumonia. Lancet 2015; 386(9998): 1097-1108.

Pschyrembel Online. 2021.

Robert Koch-Institut (RKI). SARS-CoV-2 Steckbrief zur Coronavirus-Krankheit-2019 (COVID-19). 07.08.2020.

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Created on May 11, 2022
Next planned update: 2025

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Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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