What is pneumonia?
Pneumonia is a serious infection that affects the lungs. Most cases (70% to 80%) are acquired in the community, not in a hospital or nursing home, and develop in people over age 60 or in people who have an underlying medical condition.

Pneumonia can develop in healthy younger people during the winter months, causing a mild illness with recovery in 2 to 3 weeks. Pneumonia also may occur after a viral respiratory illness; in these cases, bacteria may cause the infection, which can be severe. Recovery may take 6 to 8 weeks or longer.

What causes pneumonia?
Pneumonia is caused by viruses, bacteria, or (in rare cases) parasites or other organisms. In up to 65% of cases, the organism (such as bacteria or virus) that is causing pneumonia is not identified even with testing.

Pneumonia usually starts when a person inhales infected air particles into the lungs.

In other cases, it develops during or after a viral upper respiratory infection, such as a cold or the flu. Pneumonia also may occur as a complication of a viral illness such as measles or chickenpox.

Pneumonia can develop if a person inhales food, vomit, or mucus into the lungs (aspiration pneumonia).

What are the symptoms of pneumonia?
Pneumonia caused by bacteria usually begins suddenly and often develops during or after an upper respiratory infection, such as influenza or a cold. Symptoms of bacterial pneumonia may include:

Cough, often producing discolored mucus (sputum) from the lungs.

Sputum may be rusty or green or tinged with blood.

Fever, which may be less common in older adults.

Shaking, teeth-chattering chills (a single episode or many attacks).
Rapid, often shallow, breathing.

Chest wall pain that is often made worse by coughing or breathing in.
Rapid heartbeat.

Fatigue or vague feeling of weakness (malaise).

Shortness of breath.

Symptoms of viral pneumonia may come on gradually and are often less obvious and less severe than those of bacterial pneumonia. Viral pneumonia often goes unrecognized because the person may not appear ill.

How is pneumonia diagnosed?
Diagnosis of pneumonia is usually made from a medical history, a physical exam, and a chest X-ray. A chest X-ray usually is done to look for changes in the lungs that may indicate pneumonia, other causes of symptoms, or complications of pneumonia.

Based on the findings of the history, exam, and the chest X-ray, a doctor may choose to begin treatment right away without doing other tests. The need for more tests often is guided by the severity of symptoms, a person's age, and state of health. In general, the sicker a person is, the more tests may be done. This is particularly true for older adults and infants.

A sample of mucus (sputum) from the lungs may be examined to find out what organism is causing pneumonia. A test called a culture and sensitivity also may be done to help identify the organism. Identification helps the doctor choose the best antibiotic to treat the infection.

How is pneumonia treated?
Antibiotics are used to treat bacterial pneumonia. Hospitalization usually is not needed in younger people with strong immune systems who respond well to antibiotics and can take them by mouth.

No medication is available to treat viral pneumonia caused by viruses, except for acyclovir, which can be used in the rare cases of pneumonia caused by chickenpox (varicella).

Some people may need to be hospitalized, such as those older than 65, those who have a weakened immune system or another serious illness, or those who need to take antibiotics intravenously or who do not improve with antibiotic treatment outside the hospital.

Can pneumonia be prevented?
A pneumococcal vaccine can reduce the risk of serious complications of bacterial pneumonia caused by Streptococcus pneumoniae. However, the vaccine does not provide protection against complications caused by other forms of bacteria or viruses.

The vaccine is recommended for people over age 65 and for those who would be at increased risk for complications of pneumonia such as a secondary bacterial lung infection after a viral infection or infection caused by swelling of the covering of the spinal cord (meningitis).

Healthy older adults usually need only one shot for lifetime protection. People with a chronic medical problem are encouraged to have the vaccine every 5 to 6 years. Some health professionals recommend that everyone over the age of 65 receive the vaccine every 5 years.

The American Academy of Pediatrics recommends that children under age 2 receive the pneumococcal vaccine.

The influenza vaccine also is recommended - especially for older adults or those who have chronic medical illnesses - because it reduces the chance of getting the flu, which can lead in some cases to bacterial pneumonia.