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Learn About Pneumonia

Pneumonia is a common lung infection caused by bacteria, a virus or fungi. It is often spread via coughing, sneezing, touching or even breathing, and those who don't exhibit symptoms can also spread the illness.

Key Facts

  • Pneumonia is an infection in your lungs
  • It may be a complication of the flu
  • Most healthy people recover from pneumonia in 1 to 3 weeks, but it can be life-threatening
  • One form of bacterial pneumonia can be prevented by getting vaccinated and practicing good health habits

What Is Pneumonia?

Pneumonia is an infection in one or both of your lungs. Many germs, such as bacteria, viruses, and fungi, can cause pneumonia. Pneumonia is not a single disease. It can have more than 30 different causes. Understanding the cause of pneumonia is important because pneumonia treatment depends on its cause.

Approximately one-third of the pneumonia cases in the United States each year are caused by viruses. These viruses are the most common cause of pneumonia in children and young adults.

The flu virus is a common cause of viral pneumonia in adults. Other viruses that cause pneumonia include respiratory syncytial virus (RSV), rhinovirus, herpes simplex virus, severe acute respiratory syndrome (SARS) virus, and more.

Learn more about what causes pneumonia.

How Does Pneumonia Affect Your Body?

Most of the time, your nose and airways filter germs out of the air you breathe. This keeps your lungs from becoming infected. But germs sometimes find a way to enter the lungs and cause infections. This is more likely to occur when:

  • Your immune system is weak.
  • A germ is very strong or present in large amounts.
  • Your body fails to filter germs out of the air you breathe.

When the germs that cause pneumonia reach your lungs, the lungs' air sacs (alveoli) become inflamed and fill up with fluid. This causes the symptoms of pneumonia, such as a cough, fever, chills, and trouble breathing.

When you have pneumonia, oxygen may have trouble reaching your blood. If there is too little oxygen in your blood, your body cells can't work properly. Because of this and the risk of the infection spreading through the body, pneumonia can cause death.

Pneumonia affects your lungs in two ways. It may be in only one part, or lobe, of your lung, which is called lobar pneumonia. Or, it may be widespread with patches throughout both lungs, which is called bronchial pneumonia (or bronchopneumonia).

How Serious Is Pneumonia?

Pneumonia is a serious lung disease that kills thousands every year and hospitalizes many more.

Pneumonia tends to be more serious for infants and young children, older adults (people 65 years or older), people who have other chronic health problems, and people who have weak immune systems as a result of diseases or other factors.

If you develop pneumonia, your chances of a fast recovery are greatest if:

  • You are young
  • Your pneumonia is caught early
  • Your immune system—your body's defense against disease—is working well
  • The infection hasn't spread
  • You are not suffering from other illnesses

With treatment, most patients will improve within one to three weeks. Elderly or debilitated patients may need longer treatment.

Learn more about diagnosis and treatment of pneumonia.

    Webpage Resource

    Five Facts You Should Know About Pneumonia

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    Reviewed and approved by the American Lung Association Scientific and Medical Editorial Review Panel. Last reviewed March 30, 2018.

    Page Last Updated: April 2, 2018

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