Pneumonia is an infection or inflammation of the lungs. It can be in just one part of the lungs, or it can involve many parts. Pneumonia is caused by bacteria, viruses, fungi, and other microorganisms. The severity of pneumonia depends on which organism is causing the infection. Viral pneumonias are usually not very serious, but they can be life-threatening in very old and very young patients, and in people whose immune systems are weak.
Even severe acute respiratory syndrome (SARS), which is believed to have a viral cause, has caused very few deaths.
Influenza A and B usually occur in the winter and spring. In addition to the respiratory symptoms, you can get a headache, fever, and muscle aches. Your chance of catching the flu falls a lot (but is not totally prevented) if you get a "flu shot" every year.
Respiratory syncytial virus (RSV) is most common in the spring. It usually infects children and can cause outbreaks in daycare centers.
Herpes or varicella pneumonia are rare unless you are infected with chickenpox.
Symptoms of pneumonia caused by a virus usually go on for several days to a few weeks before you call your doctor. Most people with bacterial pneumonia get sick very quickly and see a doctor within a few days.
When to Seek Medical Care
Go to your hospital's emergency department or call your doctor if you develop any of these symptoms:
Shortness of breath, either at rest or with just a little exertion