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    Understanding Pneumonia -- the Basics

    What Is Pneumonia?

    Pneumonia is an acute infection of the lungs. It's a more common problem than most people think. Usually pneumonia is a mild disease, but some forms are very dangerous and require a hospital stay. In all cases, you'll need to seek care from your health care provider.

    Pneumonia can affect just one lobe of the right or left lung, a whole lung, or both lungs.

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    Many different kinds of germs infect the lungs and cause pneumonia. Infected lungs leak fluids and shed dead cells. This material clogs up air sacs and makes it hard for the lungs to do their job of getting oxygen into the blood. Without enough oxygen, none of the cells in your body work as they should.

    Pneumonia generally lasts about two weeks. However, you may feel tired or weak for a month or more after the lungs clear up.

    What Causes Pneumonia?

    Usually the inflammation is caused by a bacterial infection, but it can also be caused by a virus, fungus, or parasite.

    Many of these germs are all around us. They usually can't get past a healthy person's natural defenses. Pneumonia is most common in those with weaker or compromised immune systems, such as elderly people, cigarette smokers, alcoholics, and people suffering from other diseases such as the flu.

    WebMD Medical Reference

    Reviewed by Lisa Bernstein, MD on March 18, 2015

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