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Thu 2 Aug 2007 12:00 AM

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Still a threat

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.

Today, vaccines, antibiotics, and improved supportive care mean doctors can do a lot more about pneumonia.

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 categorised 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.

Symptoms and diagnosis

Pneumonia symptoms include a cough with sputum (sticky mucus from the lungs); chest pain that gets worse when inhaling; shortness of breath and overall difficulty breathing; and fever, sometimes with chills, although older people often don't mount a fever. Feelings of extreme fatigue or exhaustion are common.

"Walking pneumonia" is a nickname for any mild case that usually doesn't require hospitalisation or bed rest. Even at its mildest, pneumonia is much more than just a bad cold. Like many other conditions caused by infection, pneumonia is far more serious for the very old and young, and for those with weakened immune systems.

Doctors diagnose pneumonia based on symptoms and a physical examination. They'll use a stethoscope to listen for abnormal breathing sounds, which may lead to a different diagnosis, such as bronchitis. Diagnostic tests may include chest x-rays, blood tests, and sputum cultures to look in the mucus a patient coughs up for the organism causing the infection.

Treatment

Treatment varies according to the underlying cause. Bacterial pneumonia, the most common type in adults, is treated with antibiotics. Viral pneumonia - responsible for about half of all cases - is most common in children. Characterised by a fairly dry cough and infamous flu-like symptoms, it doesn't respond to antibiotics but is generally less serious than the bacterial form. Mainstays of treatment are rest and plenty of fluids. If the pneumonia is the direct result of a flu infection, physicians may prescribe antiviral medications. In those cases, the trick is to catch it early. Fungal pneumonia is less common than bacterial or viral forms. There are some regional variations.
Prevention

Modern medicine does much better in one-on-one contests, taking on illnesses caused by a single organism. Pneumonia is more of a pathogenic team sport. The pneumococcal vaccine (PPV23) targets 23 variants of Streptococcus pneumoniae (also known as pneumococcus), the bacterium responsible for a quarter of community-acquired pneumonia cases. Even so, the vaccine doesn't provide protection against all the pneumococcus variants, nor against other types of bacterial infections or the viral and fungal causes of pneumonia. People sometimes make the mistake of viewing the pneumococcal vaccine as the pneumonia vaccine; it's not. Moreover, novel causes of pneumonia keep appearing, such as the virus that causes SARS and the H5N1 bird flu virus.

Steps you can take

Pneumonia is far more serious for the very old and young.

1.Get the pneumococcal vaccine. Although the pneumococcal vaccine doesn't offer across-the-board protection, it's certainly the best first step you can take to avoid getting pneumonia. In the United States, though, the vaccine is recommended only for certain groups: People age 65 and over, and those deemed at high risk of getting a pneumococcal infection, a large group that includes nursing home residents and people with cardiovascular disease, diabetes, compromised immune systems, or certain chronic respiratory problems. With age, the immunity conferred by the vaccine tends to wear off faster, so some doctors recommend that older people get vaccinated every five years.

2.Get a flu shot. Flu leads to pneumonia directly and indirectly. Federal guidelines recommend that everyone over age 49 get a flu shot every year. Adults with risk factors for pneumonia, such as asthma and chronic obstructive pulmonary disease, should also get annual flu shots.

3.Stop smoking. Damage from smoking may impair the ability of the lungs to get rid of microbes that would normally be harmless but instead get trapped, causing pneumonia.

4.Don't delay in getting medical attention. If you think you might have pneumonia, see a doctor. The earlier you're diagnosed and treated, the better your chances for a full and speedy recovery.

Flu and pneumonia: what’s the connection?Flu viruses can cause pneumonia directly if their surfaces are equipped with structures that allow them to attach to receptors in the lung.

Not all flu viruses have those structures. But any flu virus is capable of weakening the lung's defences so that a bacterial infection develops and causes pneumonia. The Staphylococcus - or staph, for short - bacterial infections that cause many skin infections can cause a particularly severe form of bacterial pneumonia if they get into the lungs. Staph infections were responsible for many deaths in the 1918 flu pandemic and still cause some flu deaths every winter.

When the flu virus causes pneumonia directly, it's really the immune response that causes much of the damage, bringing fluid and cells into the alveoli of the lungs. Both the 1918 virus and today's H5N1 bird flu virus cause a dramatic immune response that is exponentially larger than the response to the typical flu virus. It's probably this strong immune response that makes the death rate from infection by those two viruses so much higher than the rate for normal flu.

This article is provided courtesy of Harvard Medical International. © 2007 President and Fellows of Harvard College.

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