An Overview of Pneumonia

Causes, Symptoms, and Treatment

woman coughing
Pneumonia often comes with a persistant cough. BSIP / UIG / Getty Images

Pneumonia is an infection deep in the lungs affecting small air sacs called the alveoli. Pneumonia causes the air sacs to become inflamed and often filled with pus. Pneumonia also affects the tiny airways that lead into the alveoli, causing them to swell closed and obstruct air flow.

Causes of Pneumonia

Pneumonia is most often caused by bacteria. About a third of the cases of pneumonia in the U.S. come from viruses.

The bacteria or virus gets trapped deep in the lungs, in the small air sacs known as alveoli. The immune system starts fighting the germs and causes inflammation.

Sometimes pneumonia follows another infection, like a cold or the flu. However, pneumonia can come on all by itself, without any other illness.

Some people are more at risk for pneumonia. The elderly and those with weakened immune systems are the most vulnerable.

A small number of pneumonia cases come from fungal infections. A common fungus is responsible for a condition called pneumocystis jiroveci or pneumocystis carinii pneumonia (PCP). Generally, PCP only affects people with weak immune systems, like patients with HIV/AIDS or people who've had organ transplants.

Signs and Symptoms of Pneumonia

The signs and symptoms of pneumonia come from both the infection and the reaction in the lungs, which interferes with air flow.

The National Heart Lung and Blood Institute suggests going to the doctor if you have these symptoms:

  • high fever (over 103 degrees)
  • chills with shaking or shivering
  • coughing up phlegm or mucus
  • shortness of breath with normal activity (get winded easily)
  • chest pain with breathing or coughing
  • suddenly feel worse after a cold or the flu

The more of these symptoms you have, the more likely your doctor will think it's pneumonia.

However, many of these symptoms are common in infections. Don't assume you have pneumonia just because you have a fever or chills, which often go together. Make sure to see your doctor if you have shortness of breath with any of these symptoms.

Treatment for Pneumonia

The most important treatment for pneumonia is to recognize the symptoms of pneumonia and contact your doctor. Pneumonia treatment often requires antibiotics or other prescription medications, depending on the cause of the pneumonia. Pneumonia treatment at home focuses on treating the cause and coping with the symptoms, especially shortness of breath.

Plus, call 911 anytime you have shortness of breath that won't go away after a few minutes of rest.


"Pneumonia." NIH: National Heart Lung and Blood Institute. Last updated: Aug 2008. Accessed 3 Sep 2010