Mayo Clinic Health Manager
Get free personalized health guidance for you and your family.
Get Started
About our e-newsletters
- Free e-newsletters
- Mayo Clinic expertise
- We do not share your e-mail address
Housecall, our weekly general-interest e-newsletter, keeps you up to date on a wide variety of health topics with timely, reliable, practical information, recipes, blogs, questions and answers with Mayo Clinic experts and more. Our biweekly topic-specific e-newsletters also include blogs, questions and answers with Mayo Clinic experts, and other useful information that will help you manage your health.
Housecall Archives
Mayo Clinic Housecall
Stay up to date on the latest health information.
What you get
- Free weekly e-newsletter
- Mayo Clinic expertise
- Recipes, tools and other helpful information
- We do not share your e-mail address
Causes
By Mayo Clinic staff
Your body has ways to protect your lungs from infection. In fact, you're frequently exposed to bacteria and viruses that can cause pneumonia, but your body normally uses a number of defenses, such as cough and the normal microorganisms (flora) in your body, to prevent harmful organisms from invading and overwhelming your airways. However, numerous conditions, including malnutrition and systemic illness, can lower your protection and allow harmful organisms to get past your body's defenses and into your lungs.
Once the invading organisms are in your lungs, white blood cells — a key part of your immune system — begin to attack them. The accumulating invaders, white blood cells and immune system proteins cause the tiny air sacs in your lungs to become inflamed and filled with fluid, leading to the difficult breathing that characterizes many types of pneumonia.
Classifications of pneumonia
Pneumonia is sometimes classified according to the cause of pneumonia:
- Community-acquired pneumonia. This refers to pneumonia you acquire in the course of your daily life — at school, work or the gym, for instance. The most common cause is the bacterium Streptococcus pneumoniae. Another, less common cause is Mycoplasma pneumoniae, a tiny organism that typically produces milder signs and symptoms than other types of pneumonia. Walking pneumonia, a term used to describe pneumonia that isn't severe enough to require bed rest, may result from Mycoplasma pneumoniae.
-
Hospital-acquired (nosocomial) pneumonia. If you're hospitalized, you're at a higher risk of pneumonia, especially if you're breathing with the help of a mechanical ventilator, in an intensive care unit or have a weakened immune system. This type of pneumonia can be extremely serious, especially for older adults, young children and people with chronic obstructive pulmonary diseases (COPD) or HIV/AIDS.
Hospital-acquired pneumonia develops at least 48 hours after you're admitted to the hospital. This category includes post-operative pneumonia — most common in people older than age 70 who have abdominal or chest surgery — and health-care associated pneumonia — acquired in chronic care facilities, centers where drugs are given by intravenous drip (infusion) and kidney dialysis centers.
A common predisposing factor for this type of pneumonia is gastroesophageal reflux disease (GERD). This occurs when some of the contents of your stomach flow back into the upper esophagus. From there, the gastroesophageal contents can be inhaled (aspirated) into your windpipe and then into your lower airways. Even small amounts of gastroesophageal reflux can lead to pneumonia in people who are hospitalized.
-
Aspiration pneumonia. This type of pneumonia occurs when you aspirate foreign matter into your lungs — most often when the contents of your stomach enter your lungs after you vomit. This commonly happens when a brain injury or other condition affects your normal gag reflex.
Another cause of aspiration pneumonia is consuming too much alcohol. Aspiration occurs when the inebriated person passes out and then vomits due to the effects of alcohol on the stomach. If someone's unconscious, it's possible to aspirate the liquid contents and possibly solid food from the stomach into the lungs, causing aspiration pneumonia.
Difficulty swallowing, which occurs with diseases such as amyotrophic lateral sclerosis (ALS), Parkinson's disease and strokes, may also lead to aspiration pneumonia.
- Pneumonia caused by opportunistic organisms. This type of pneumonia strikes people with weakened immune systems. Organisms that aren't harmful for healthy people can be dangerous for people with AIDS and other conditions that impair the immune system, as well as people who have had an organ transplant. Medications that suppress your immune system, such as corticosteroids or chemotherapy, also can put you at risk of opportunistic pneumonia.
- Other pathogens. Outbreaks of the H5N1 influenza (bird flu) virus and severe acute respiratory syndrome (SARS) have caused serious, sometimes deadly pneumonia infections, even in otherwise healthy people. Although rare, anthrax, plague and tularemia also may cause pneumonia. Some forms of fungi, when inhaled can cause pneumonia. Tuberculosis in the lung also can cause pneumonia.
- Pneumonia. The Merck Manuals: 00The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/sec05/ch052/ch052a.html. Accessed March 25, 2009.
- Pneumonia fact sheet. American Lung Association. http://www.lungusa.org/site/apps/nlnet/content3.aspx?c=dvLUK9O0E&b=2060321&content_id={08C669B0-E845-4C9C-8B1E-285348BC83BD}¬oc=1. Accessed March 28, 2009.
- Durrington H, et al. Recent changes in the management of community-acquired pneumonia in adults. British Medical Journal. 2008;336:1429.
- Pneumonia. American Lung Association. http://www.lungusa.org/site/apps/nlnet/content3.aspx?c=dvLUK9O0E&b=4294229&ct=3052571. Accessed March 28, 2009.
- Menendez R, et al. Treatment failure in community-acquired pneumonia. Chest. 2007;132:1348.
- Singh S, et al. Long-term use of inhaled corticosteroids and the risk of pneumonia in chronic obstructive pulmonary disease: A meta-analysis. Archives of Internal Medicine. 2009;169;219.
- Chong C, et al. Pneumonia in the elderly: A review of the epidemiology, pathogenesis, microbiology and clinical features. Southern Medical Journal. 2008;101;1141.
- Chong C, et al. Pneumonia in the elderly: A review of severity assessment, prognosis, mortality, prevention and treatment. Southern Medical Journal. 2008;101;1134.
