Causes of Pneumonia

Viruses, bacteria, and fungi can all cause pneumonia. In the United States, common causes of viral pneumonia are

  • Influenza viruses
  • Respiratory syncytial virus (RSV)
  • SARS-CoV-2 (the virus that causes COVID-19)

Common causes of bacterial pneumonia are Streptococcus pneumoniae (pneumococcus) and, especially in kids, Mycoplasma pneumoniae.

The bacteria and viruses that most commonly cause pneumonia in the community are different from those in healthcare settings. However, clinicians are not always able to find out which germ caused someone to get sick with pneumonia.

Defining Types of 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 setting. Healthcare settings 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.

Learn more below about the infections that commonly cause pneumonia.