Causes of Pneumonia

Some patients with coronavirus disease 2019 (COVID-19) have had pneumonia. Learn more about COVID-19.

Common Causes of Pneumonia

Viruses, bacteria, and fungi can all cause pneumonia. In the United States, common causes of viral pneumonia are influenza and respiratory syncytial virus (RSV). A common cause of bacterial pneumonia is Streptococcus pneumoniae (pneumococcus). However, clinicians are not always able to find out which germ caused someone to get sick with pneumonia.

Community-acquired pneumonia is when someone develops pneumonia in the community (not in a hospital). Healthcare-associated pneumonia is when someone develops pneumonia during or following a stay in a healthcare facility. Healthcare facilities include hospitals, long-term care facilities, and dialysis centers. Ventilator-associated pneumonia is when someone gets pneumonia after being on a ventilator, a machine that supports breathing. The bacteria and viruses that most commonly cause pneumonia in the community are different from those in healthcare settings.

Learn more below about the infections that commonly cause pneumonia.

Human Metapneumovirus (HMPV) Infection
Human Parainfluenza Virus (HPIV) Infection
Influenza (Flu)
Legionnaires' Disease
Mycoplasma Pneumoniae Infection
Pneumococcal Disease
Pneumocystis Pneumonia
Respiratory Syncytial Virus (RSV) Infection
Rhinovirus Infection
Page last reviewed: March 9, 2020