Despite advances in antibiotic therapy, pneumonia remains one of the leading causes of death in the United States. Unlike bronchitis, which affects the air passages that head to the lung, pneumonia is an infection of the lung tissue itself. It can be due to viruses, such as the influenza virus, a fungus, or bacteria. Most clinically significant pneumonias are due to bacterial infections, thus this will be the focus of this article.

According to Up to Date, each year, approximately four million cases of pneumonia are acquired in the community setting (also called community acquired pneumonia, or CAP). Of these, close to 20 percent require hospitalization. That number is on top of those cases of pneumonia that occur while in the hospital, nursing home, or other long-term care facilities.

The distinction between CAP and other forms of pneumonia is significant because people who develop pneumonia while going about their regular day to day activities are likely to be infected with an organism that is easier to treat than those who develop their pneumonia while in a hospital setting for example. (People in the hospital are, by definition, sicker than those at home and they are exposed to more really bad organisms, despite the best hygiene efforts of doctors and staff.)

While CAP can be caused by several different types of bacteria, by far, the majority are caused by bacteria called Streptococcal pneumonia, also called the pneumococcus.

How could I come down with pneumonia?
Each time we take in a breath, we are exposed to tiny microorganisms around us. Normally, the body is able to prevent these microorganisms from invading the lung tissue and setting up pneumonia. Some natural defenses we have include our immune systems and tiny hair-like particles that line the airways. Despite these natural defense mechanisms, occasionally these microorganisms are able to "set up shop" in the lungs and replicate over and over again, thus causing pneumonia.

Am I at risk for pneumonia?
Anyone can develop pneumonia, but there are certain groups who are at particularly high risk. These include, but are not limited to the following:
Those over 65 years old
The very young
Cigarette smokers
Individuals with chronic diseases, such as asthma, COPD, diabetes, and heart failure
Those who are malnourished
Bedridden individuals and others who have an impaired ability to cough, such as stroke patients
People whose immune system is impaired, such as from chemotherapy or steroid use

What are the symptoms of pneumonia?
Common symptoms include:
Cough, particularly a cough that produces yellow, green, or rust colored sputum
Fever (less common in elderly than in the young)
Chills
Shortness of breath
Chest pain, especially upon breathing
Nausea, vomiting, and/or diarrhea (not as likely due to pneumonia if there are no respiratory symptoms at all)
Mental status changes (such as confusion)

Can I prevent pneumonia?
The pneumococcal vaccine can significantly decrease your changes of getting a severe case of Streptococcal pneumonia, the most common form of pneumonia. However, there are no effective vaccines for the other bacteria that can cause pneumonia.

Wash your hands frequently.

Avoid close contact with people who are sick with a respiratory illness.

How is it treated?
Pneumonia is treated with antibiotics, and typically people start to feel better within a few days of starting therapy, though a minority of people develop complications of pneumonia. Not all people need to be hospitalized when they have pneumonia, but it is important to seek medical attention early if you have worrisome symptoms. The sicker you are when you see your doctor, the more likely it is you will require hospitalization and develop complications of pneumonia.