Overview of Pneumonia

Pneumonia is a general term that means inflammation of the lungs. It can affect one or both of the lungs. If bacteria, a virus, a fungus, or other foreign matter enters the lungs, the body’s natural immune response produces inflammation in the affected area. When inflammation occurs in the lungs, fluid and pus (destroyed white blood cells) can collect and interfere with normal lung function, which is to provide oxygen to and remove carbon dioxide from the bloodstream.

Pneumonia ranges in severity from mild to severe, and it can be fatal. Very young children, adults over 65, and patients who have a chronic illness are particularly vulnerable to pneumonia. In patients who are at increased risk for this condition, talking with a qualified health care provider about precautions and taking steps to prevent pneumonia can help reduce the risk.

Incidence and Prevalence of Pneumonia

In the United States, about 3 million cases of pneumonia are reported each year and about 60,000 people die as a result of the condition. About one-third of pneumonia cases occur in people over age 65. Approximately 4 out of every 100 children in the United States develop pneumonia each year.

Pneumonia Causes and Risk Factors

There are many different types of pneumonia, and vaccines are available to protect against some types. The most common types are caused by either a bacterial or viral infection.

Bacterial pneumonia is usually transmitted from person to person through coughing or sneezing. However, Legionnaires disease is a type of bacterial pneumonia that is transmitted by breathing in water vapor contaminated with Legionella bacteria. This strain of bacteria is sometimes found in the plumbing and air conditioning systems of large buildings or in poorly maintained hot tubs. This type of pneumonia does not spread from person to person.

Viruses, such as the influenza (flu) virus and the common cold virus, are the most common cause of pneumonia in young children and the elderly. Measles and chickenpox (i.e., varicella-zoster virus) also can develop into pneumonia.

Mycoplasma, which is a group of bacteria, is another type of organism that can cause pneumonia. Because it is highly contagious, this type usually occurs in older children and young adults in school or other group settings.

Breathing in (inhaling) dust, contaminated liquids, gases, or even food also can cause pneumonia. Patients who require assisted breathing and are put on a ventilator can accidentally inhale food or vomit into the lungs. This kind of inhalation also occurs in people who pass out from drinking excessive amounts of alcohol and in patients whose gag reflex is impaired (e.g., due to a brain injury).

People with weakened immune systems, such as patients who have HIV or other chronic health conditions, and patients who have received an organ transplant, are at increased risk for pneumonia. Patients with these conditions can develop pneumonia from viruses that usually do not affect healthy people.

The following medical conditions increase the risk for pneumonia:

  • Diabetes
  • Emphysema
  • Heart disease
  • HIV/AIDS
  • Sickle-cell disease

Others who are at increased risk include patients who are taking immunosuppressant drugs, post-operative patients with an impaired ability to cough or clear the lungs, patients in intensive care units (ICUs) who are on breathing tubes, patients who have their spleen removed, and patients who are undergoing chemotherapy.

The following people also are at increased risk for developing pneumonia:

  • Adults over 65 years old
  • Infants and very young children who have immature immune systems
  • People who live in areas with high levels of air pollution
  • Farm workers exposed to agricultural chemicals
  • Construction workers and workers in industrial settings
  • People who work near animals
  • People who smoke or are addicted to alcohol

Patients who are at increased risk should talk with a qualified health care provider about ways to reduce the risk for developing pneumonia.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 24 Sep 2007

Last Modified: 01 Oct 2015