An update on the "old man's friend".(pneumonia)

The flu and pneumococcal vaccines provide some protection against it, but pneumonia is still a major cause of death.

Pneumonia is inflammation deep inside the lungs caused by some kind of infection. As a result of the infection and the immune response to it, the tiny air sacs (alveoli) -- where oxygen is absorbed into the bloodstream -- fill with fluid, impairing the ability to breathe. Each year millions of Americans come down with a case, frequently as a complication of another illness, and about 60,000 die from pneumonia.

Doctors once had little choice but to be fatalistic about deaths from pneumonia. Sir William Osler, sometimes called the father of modern medicine, famously called it "friend of the aged" (often rendered as "the old man's friend") because it was seen as a swift, relatively painless way to die. But that was over 100 years ago. Today, vaccines, antibiotics, and improved supportive care mean doctors can do a lot more about pneumonia, although it remains a major killer, capable of thwarting the best efforts at prevention and treatment.

Many causes and categories

Pneumonia isn't caused by just one or two types of infection. Any of about 100 different bacteria, viruses, and fungi can lead to pneumonia, although a relative handful account for most cases.