Causes of Pneumonia

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

HMPV is an important cause of upper and lower respiratory illness, such as pneumonia…

Human Parainfluenza Virus (HPIV) Infection

HPIVs commonly cause upper and lower respiratory illness, such as pneumonia, in children and adults…

Influenza (Flu)

The flu is a contagious respiratory illness caused by influenza viruses that can cause mild to severe illness…

Legionnaires' Disease

Legionnaires’ disease is a severe type of pneumonia caused by bacteria called Legionella

Mycoplasma Pneumoniae Infection

This generally mild illness, caused by the bacteria Mycoplasma pneumoniae, is a common cause of “walking pneumonia”…

Pneumococcal Disease

The bacteria Streptococcus pneumoniae, also known as pneumococcus, cause pneumococcal disease…

Pneumocystis Pneumonia

A fungus called Pneumocystis jirovecii can cause pneumocystis pneumonia, a serious illness in people with weakened immune systems…

Respiratory Syncytial Virus (RSV) Infection

RSV is the most common cause of bronchiolitis and pneumonia in children younger than 1 year old. But you can get RSV at any age…

Rhinovirus Infection

Rhinoviruses frequently cause mild illness like the common cold, but they can also cause serious lower respiratory illness like pneumonia…

Page last reviewed: October 22, 2018