Skip to main content


Pneumonia has many different causes. Many different germs can cause pneumonia, including bacteria, viruses, and fungi. You can also get it from breathing in (aspirating) food, liquid, chemicals and dust.

If you have pneumonia caused by a virus it is called viral pneumonia. Many different viruses can cause viral pneumonia, including the flu (influenza) and RSV (respiratory syncytial virus), a virus that is common in children. Viral pneumonia is usually less serious than bacterial pneumonia.

Viral pneumonia can be life threatening in:

  • seniors and infants
  • people who have a weak immune system from diseases like chronic lung disease, HIV, cancer and diabetes
  • pregnant women

If you have pneumonia caused by bacteria it is called bacteria pneumonia. The most common type of bacterial pneumonia is Streptococcus pneumoniae (pneumococcus). Other bacteria that cause pneumonia include: mycoplasma pneumoniae, chlamydia pneumoniae and legionella pneumophila.

Bacterial pneumonia usually affects an entire lobe of the lung; doctors call this lobar pneumonia. People of any age can get it.

Other types of pneumonia include aspiration pneumonia. You can get aspiration pneumonia if you breathe (aspirate) something into your lungs, for example vomit, food or dust. Vomit is the most common cause of aspiration pneumonia. This can happen when people are unconscious or semi-conscious (knocked out) because of a stroke, accident or alcohol or drug overdose. Other things that can cause aspiration pneumonia include:

  • liquid (for example, water)
  • dust
  • fungus

Other types of pneumonia include pneumocystis jiroveci that is a type of fungus commonly found in the environment. It can cause pneumonia in people with weak immune systems. It is most common in people with HIV/AIDS, diabetes, sickle cell and lung disease, and in people whose immune systems are weak from taking cancer treatment. Healthy people rarely get sick from breathing in the Pneumocystis jiroveci fungus.

If you have a weak immune system because of a chronic disease (for example, lung disease or HIV) and you get a cough, fever and/or shortness of breath, call your doctor.

Risk factors that increase your chances of getting pneumonia include:

  • Chronic lung disease (COPD, asthma, cystic fibrosis)
  • Cigarette smoking
  • Dementia, stroke, brain injury, cerebral palsy, or other brain disorders
  • Immune system problem (during cancer treatment, or due to HIV/AIDS, organ transplant or other diseases)
  • Other serious illnesses, such as heart disease, liver cirrhosis, or diabetes mellitus
  • Recent surgery or trauma
  • Surgery to treat cancer of the mouth, throat, or neck