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.

To further complicate matters, pneumonia is categorized in many different ways -- by cause (bacterial, viral, or fungal), affected area (lobar pneumonia involves one lobe or part of a lung; bronchopneumonia extends generally throughout the lung; double pneumonia affects both lungs), or where or how it was contracted. People who get pneumonia in their regular, day-to-day activities have community-acquired pneumonia. Catching pneumonia in a hospital (hospital-acquired pneumonia) tends to be quite serious because hospital bacteria are often resistant to antibiotics. Aspiration pneumonia results from inhaling food, vomit, or other foreign material into the lungs, which occurs when the gag reflex is impaired from, for example, excessive alcohol or sedative use, or having had a stroke.

Some cases of pneumonia are identified by the particular pathogens that cause them. Legionnaire's disease is any respiratory infection caused by the bacterium Legionella pneumophila. Sometimes people only experience a mild cough, but Legionella pneumophila is capable of causing serious, even fatal, pneumonia. Pneumocystosis is a pneumonia caused by the fungal organism Pneumocystis carinii, now officially renamed Pneumocystis jiroveci. Pneumocystis jiroveci is ubiquitous and doesn't usually cause illness. But in people with weakened immune systems -- those with cancer or HIV/AIDS, or who are taking immunosuppressant drugs after an organ or bone marrow transplant -- infection with the organism may result in pneumonia.