Pneumonia 2364
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Pneumonia is inflammation of the lungs. It is a common illness usually caused by infection with a bacterium, virus, or fungus. It is often mild, especially in young people, and is usually curable or goes away on its own. Pneumonia may cause serious illness, especially in people who are old or already have health problems, and it remains a major cause of death.


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Respiratory system

What Is Pneumonia?

Each day a person inhales large amounts of air, often laden with germs, dust, and other partides. The air is drawn deep into the lungs, two spongy air sacs in the chest where oxygen from the air is transferred to the blood. Yet despite the constant chance of inhaling germs, the lungs of a healthy person are basically sterile, meaning germ-free. How is this possible? An array of natural defenses protects these crucial organs from infection. These defenses indude:

  • The ability to cough deeply. This expels germs and keeps germ-trapping mucus from building up in the lungs.
  • The vocal cords and the epiglottis (ep-i-GLOT-is), a flap of tissue that closes the trachea (TRAY-ke-a or windpipe) when a person swallows. These, along with the gag reflex, keep people from inhaling food, vomit, or stomach acid into their lungs.
  • The cilia (SILL-ee-a), small hairs that line the inside of the wind-pipe, waving upward. They filter particles out of the air before they reach the lungs.
  • The immune system, a complex set of organs, chemicals, and white blood cells that attack germs that may enter the body.

These defenses usually prevent pneumonia, but sometimes a person's defenses may be weakened by illness, age, or other factors. The defenses also may be overwhelmed by a particularly heavy or virulent * dose of germs.

Sometimes, the germs or chemicals that cause pneumonia are aspirated or inhaled not from the air but from a person's own throat, as when germ-bearing food or vomit is breathed into the lungs. This may cause aspiration pneumonia. Sometimes the germs are not inhaled at all but enter the lungs from the bloodstream.

How Does Pneumonia Make Breathing Difficult?

When germs or chemicals irritate lung tissue, the irritation causes inflammation, a condition that includes fever and a buildup of white blood cells and mucus in the lungs. Breathing becomes more difficult. The lungs have to work harder to transfer oxygen into the bloodstream and to remove carbon dioxide, a dangerous waste product, from the blood. Eventually, the cells of the body may not get enough oxygen, and carbon dioxide may build up in the body.

Who Is at Risk for Pneumonia?

Anyone can get pneumonia, but it tends to strike people whose natural defenses against infection are weak. A growing number of people fall into that category. They may be very old, they may have AIDS (which damages the body's immune system), they may have received organ transplants (which work only if drugs are taken to weaken the immune system), or they may be living with cancer or another serious illness.

Streptococcal Pneumonia

The bacteria that cause streptococcal pneumonia, the most common kind of pneumonia, live in the upper respiratory systems of many healthy people without making them sick. However, if another illness reduces the immune system's ability to control these bacteria, they can reproduce rapidly to dangerous levels.

Sometimes a cold will be followed by streptococcal pneumonia, because the fluids produced by a cold's runny nose and sore throat make an excellent breeding ground for streptococcal bacteria. The majority of people recover fully after antibiotic treatment and bed rest.

* virulent comes from the Latin word for poisonous, and describes a microbe that is especially well suited to countering the immune system.

Patients in the hospital are at special risk for developing pneumonia, especially if they have difficulty breathing deeply or coughing, as can happen after chest or abdominal surgery. In addition, some hospital tests and treatments require tubes to be inserted into the trachea. This can give germs a way into the lungs, making pneumonia more likely. An infection acquired in the hospital is said to be "nosocomial" (no-so-KOME-ee-al), an adjective based on the Greek word for hospital.

Other people at special risk for pneumonia are:

  • Anyone who is bedridden, paralyzed, or not fully conscious, because they may lack the ability to cough or gag.
  • People with chronic (long-lasting) diseases such as diabetes, heart failure, or chronic obstructive pulmonary disease, a lung disorder.
  • People who smoke or abuse alcohol.
  • Children who have cystic fibrosis, which causes mucus to build up in the lungs.
  • Infants, because their immune systems are not fully developed.

Mycoplasma Pneumonia

Mycoplasma pneumonia is the most common form of atypical pneumonia. It affects mainly young people ages 5 to 35. It got the nickname "walking pneumonia" because it often has flu-like symptoms so mild that people keep walking around with it instead of getting bed rest.

One reason mycoplasma pneumonia tends to be mild is because the bacteria that cause it do not invade the deep tissue of the lungs. Instead, they grow on the mucous membranes that line the lungs. This does not cause as much swelling or lung inflammation as in other kinds of pneumonia.

Which Microorganisms Cause Pneumonia?

More than 75 kinds of germs can cause pneumonia. Here are some common bacterial causes:

  • Streptococcuspneumoniae is the most common cause of adult pneumonia.
  • Staphylococcus aureus causes many cases of pneumonia in the hospital. This is the same bacterium that produces staph infections.
  • Mycoplasma pneumoniae is the usual cause of atypical or "walking" pneumonia, a mild form common in young people between the ages of 5 and 35.
  • Chlamydia, Legionella, Klebsiella, Pseudomonas, and many others.

Some common viral causes that tend to affect children and the elderly are:

  • respiratory syncytial (sin-SISH-al) virus. It affects mainly babies and pre-teens, usually causing mild illness that goes away after a week or so.
  • Influenza A and B viruses. Very few people infected with flu virus develop pneumonia. Those who do, however, run a high risk of dying, especially if they are old or chronically ill. Sometimes, besides getting viral pneumonia, they get a "superinfection" or a bacterial infection in the lungs on top of the viral infection.
  • The viruses that cause measles and chickenpox, as well as other common families of viruses.
  • Epstein-Barr virus, and herpes simplex. These cause serious pneumonia most often in people with AIDS or other immune problems.

Other causes of pneumonia include:

  • Fungal pneumonia, which is seen mostly in people with AIDS or other immune-system problems. The most common fungal cause is Pneumocystic carinii (noo-mo-SIS-tik kar-RIN-ee-i) pneumonia. PCP, as it is often called, used to be the main killer of people infected with HIV, the human immunodeficiency virus that causes AIDS. Medications now can often prevent it, but it still is a serious problem.
  • Parasites, such as toxoplasma, which also can cause pneumonia.
  • Reactions to certain medications.
  • High doses of radiation or toxic chemicals if they are inhaled or aspirated.

What Happens When People Have Pneumonia?


People who have streptococcal pneumonia, the most common kind, often get a fever of 102 to 104 degrees F (39 to 40.5 degrees Centigrade) and chills that cause the body to shake. They cough, often bringing up large amounts of thick, greenish mucus, sometimes mixed with blood. They may breath more quickly, and they may have rales (pronounced "rahls"), a crackling sound that can be heard with a stethoscope. Their chests hurt, too; the stabbing pain seems to get worse the more they cough. Other symptoms include a bad headache, loss of appetite, tiredness, nausea, and vomiting.

People who are elderly or who have immune system problems often have milder symptoms in the beginning, even though their illness may be more dangerous. They might, for instance, have just a low-grade fever, tiredness, or confusion, and a sense of being ill.

People with atypical or mycoplasma pneumonia often get a dry cough, a sore throat, skin rashes, and muscle and joint pain. Because these are not the classic symptoms of pneumonia, people may think they just have a mild case of flu.

People with influenza pneumonia often have fever, a severe dry cough, rales, and severe fatigue.


If a person has persistent fever and a cough, doctors will suspect pneumonia. They may be able to diagnose pneumonia by listening through a stethoscope to the person's breathing. In any case, a chest x-ray usually makes the diagnosis clear.

The U.S. and the World

In the nineteenth century when few illnesses were treatable, pneumonia was called "the old man's friend." It won this grim nickname because it swiftly ended the lives of many old men and old women who had been suffering with other untreatable illnesses. It often was a sick person's last illness.

Today, medicine and good medical care usually cure pneumonia, even in the sick and elderly, and sometimes can prevent it as well. Yet pneumonia occurs in so many people that it still ranks as the sixth most common cause of death in the United States. An estimated 2 million Americans a year get it, and 40,000 to 70,000 die.

In many developing countries, pneumonia ranks first or second as a cause of death, along with diarrhea caused by infectious diseases.

Finding out which germ is causing the pneumonia is often much harder. Blood samples and coughed-up mucus can be tested in the laboratory. Sometimes a lung biopsy is done. This means a sample of lung tissue is removed through surgery or extracted with a needle so it can be studied. If the pneumonia has caused excess fluid around the lung, this fluid also can be sampled with a needle. Often, however, the organism is not identified at all, or is identified too late to help with decisions about treatment.


If a specific type of bacteria has been identified as the cause of the pneumonia, the doctor can prescribe antibiotic drugs that target those bacteria. If the germ is not pinpointed but bacteria are suspected, the doctor may give antibiotics that are active against the most likely causes. If the cause is a virus or fungus, antibiotics will not help. Instead, some antiviral and antifungal drugs are available, although not all viruses have treatments.

When the pneumonia is severe, people often are hospitalized. They may be given oxygen or put on a ventilator (a breathing machine) to help them breathe while the medications and the immune system fight the infection.

How Is Pneumonia Prevented?

Yearly flu vaccinations can prevent pneumonia caused by certain influenza viruses, and a one-time vaccination can help protect people against pneumococcal pneumonia.

People who have the AIDS virus can reduce their chances of getting Pneumocystic carinii pneumonia by taking daily medication. Not smoking, or quitting the habit, and not drinking alcohol excessively also can reduce the risk of pneumonia.

To prevent pneumonia in the hospital, patients are encouraged to breathe deeply, and they are sometimes given plastic breath meters that measure how well they are doing. They also are encouraged to move around, if possible, rather than staying in bed. These practices prevent the lungs from filling with mucus and other fluids that some bacteria thrive in.

How Might Pneumonia Change a Person's Life?

Most people who are treated for pneumonia recover completely in a few weeks. Some people, especially those who are old or had lung problems to begin with, may develop permanent breathing problems from scarring of the lungs. This may limit their ability to carry out their usual activities.

See also
Bacterial Infections
Chlamydial Infections
Fungal Infections
Legionnaire's Disease
Viral Infections


The American Lung Association posts a fact sheet about pneumonia at its website.

Also read article about Pneumonia from Wikipedia

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