Many germs can cause pneumonia. The most common are bacteria and viruses in the air we breathe. Your body usually prevents these germs from infecting your lungs. But sometimes these germs can overpower your immune system, even if your health is generally good.
Pneumonia is classified according to the types of germs that cause it and where you got the infection.
Community-acquired pneumonia is the most common type of pneumonia. It occurs outside of hospitals or other health care facilities. It may be caused by:
- Bacteria. The most common cause of bacterial pneumonia in the U.S. is Streptococcus pneumoniae. This type of pneumonia can occur on its own or after you've had a cold or the flu. It may affect one part (lobe) of the lung, a condition called lobar pneumonia.
- Bacteria-like organisms. Mycoplasma pneumoniae also can cause pneumonia. It typically produces milder symptoms than do other types of pneumonia. Walking pneumonia, a term used to describe pneumonia that isn't severe enough to require bed rest, may be caused by M. pneumoniae.
- Viruses. Some of the viruses that cause colds and the flu can cause pneumonia. Viruses are the most common cause of pneumonia in children younger than 5 years. Viral pneumonia is usually mild. But in some cases it can become very serious.
- Fungi. This type of pneumonia is most common in people with chronic health problems or weakened immune systems, and in people who have inhaled large doses of the organisms. The fungi that cause it can be found in soil or bird droppings.
Some people catch pneumonia during a hospital stay for another illness. This type of pneumonia can be serious because the bacteria causing it may be more resistant to antibiotics. People who are on breathing machines (ventilators), often used in intensive care units, are at higher risk of this type of pneumonia.
Health care-acquired pneumonia
Health care-acquired pneumonia is a bacterial infection that occurs in people who are living in long-term care facilities or have been treated in outpatient clinics, including kidney dialysis centers. Like hospital-acquired pneumonia, health care-acquired pneumonia can be caused by bacteria that are more resistant to antibiotics.
Aspiration pneumonia occurs when you inhale food, drink, vomit or saliva into your lungs. Aspiration is more likely if something disturbs your normal gag reflex, such as a brain injury or swallowing problem, or excessive use of alcohol or drugs.
Mar. 14, 2015
- Pneumonia. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/health-topics/topics/pnu. Accessed Jan. 20, 2015.
- AskMayoExpert. Community-acquired pneumonia. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2015.
- Longo DL, et al. Harrison's Principles of Internal Medicine. 18th ed. New York, N.Y.: McGraw-Hill; 2012. http://accessmedicine.mhmedical.com/book.aspx?bookid=331. Accessed Jan. 21, 2015.
- Schauner S, et al. Community-acquired pneumonia in children: A look at the IDSA guidelines. Journal of Family Practice. 2013;62:9.
- Attridge RT, et al. Health care-associated pneumonia: An evidence-based review. American Journal of Medicine. 2011;124:689.
- Hunter JD. Ventilator associated pneumonia. BMJ. 2012;344:e3325.
- Dockrell DH, et al. Pneumococcal pneumonia: Mechanisms of infection and resolution. Chest. 2012;142:482.
- Reynolds RH, et al. Pneumonia in the immunocompetent patient. The British Journal of Radiology. 2010;83:998.
- Rosenow EC (expert opinion). Mayo Clinic, Rochester, Minn. Jan. 20, 2015.
- Centers for Disease Control and Prevention. Adults: Protect yourself with pneumococcal vaccines. http://www.cdc.gov/features/adult-pneumococcal/. Accessed Jan. 20, 2015.
- Marrie TJ, et al. Pneumococcal pneumonia in adults. http://www.uptodate.com/home. Accessed Jan. 20, 2015.
- Barbara Woodward Lips Patient Education Center. Care following hospitalization for community-acquired pneumonia. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2013.
- AskMayoExpert. Community-acquired pneumonia (pediatric). Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2014.
- Barson WJ. Community-acquired pneumonia in children: Outpatient treatment. http://www.uptodate.com/home. Accessed Jan. 21, 2015.
You Are ... The Campaign for Mayo Clinic
Mayo Clinic is a not-for-profit organization. Make a difference today.