What is Pneumonia?

Pneumonia

What is pneumonia?

If you've been diagnosed with pneumonia, it means you've got an infection in your lungs. Pneumonia is a serious illness, and you'll feel very sick. You'll have a fever and a cough. You may also feel like you can't catch your breath. You'll be weak and tired. And you probably won't feel like eating or drinking.

You're more likely to get pneumonia if you're older than 65 or if you smoke or drink a lot. You're also more likely to get it if you've already got another serious illness that has made your body and its natural defenses against infection weaker. Children who are younger than 2 years old are also at an increased risk of getting pneumonia.

Pneumonia can be dangerous, especially if you are older or already ill. If you think you have pneumonia, you should call your doctor right away. If you get treatment quickly, and if you rest and follow your doctor's advice, you are likely to make a full recovery. If you are older or have another health condition, you may not recover as quickly as someone who is younger or healthier.

Key points for people with pneumonia

Pneumonia is serious and can sometimes kill. If you think you have it, see your doctor right away.
Most people with pneumonia can be treated at home. You need to go to the hospital only if you are very sick.
Antibiotic drugs are the main treatment for pneumonia. The sooner you take them, the better your chance of making a good recovery.
It's important to be sure that you recover completely. Go to your doctor if any symptoms, such as fever and cough, don't seem to be going away.
There are vaccines that may protect you against pneumonia. Your doctor will probably recommend getting these if you are at a high risk of getting pneumonia because you are older or in poor health. There is also a special vaccine for children. It should be given to all babies between 2 months old and 23 months old.

To learn more, see Antibiotics and Vaccines that can help protect you against pneumonia.

How do your lungs work?

You have two lungs. They sit in your chest, inside your rib cage. One sits on each side of your heart. Your lungs are a little like two spongy, elastic bags that fill up with air as you breathe in. They empty as you breathe out.

You have two lungs. They sit inside your rib cage.

A moist layer of tissue (called the pleura) covers your lungs.

Your lungs are divided into sections, or lobes. Your right lung has three lobes. Your left lung has two.

Keeping your lungs healthy is important. They supply oxygen from the air you breathe to every cell in your body. When you breathe out, they get rid of carbon dioxide, which is a waste product made by your body.

Here's how air travels into your lungs.

Your windpipe (also called the trachea) is the air passage that leads from your throat into your chest.
In your chest, it divides into two smaller airways (called bronchi). Each airway leads into a lung.
Inside your lungs, the airways divide into even smaller airways (called bronchioles). At the end of each of these smaller airways are little air sacs (called alveoli). There are about 3 million of these tiny, grapelike sacs.

Source:
National Heart, Lung and Blood Institute
The lungs in health and disease
NIH Publication No. 97-3279

¹

When you breathe in, air travels down your windpipe, through the airways, into your lungs and then into the smaller airways and the air sacs.

The air sacs in your lungs are connected to the network of blood vessels that surrounds your lungs. Oxygen from the air you breathe in passes through the thin walls of the air sacs and into these blood vessels.

When you breathe in, oxygen passes from the air sacs into your blood vessels.

Then, it is carried back to your heart and pumped around your body. At the same time, carbon dioxide (which is made as a byproduct of breathing) passes from your blood into the air sacs. The carbon dioxide leaves your body when you breathe out.

Protecting you against infection

Your lungs have another important job. They filter the air you breathe. This keeps your body from being invaded by germs and other harmful things, such as pollution. Germs are all around us. They live in the air, soil and water, and sometimes in our noses and throats. If they get into your body, they can multiply. If they do this, you can get an

infection
You get an infection when viruses, bacteria, fungi or other tiny organisms get into your body. These bugs are so tiny that you can't see them without a microscope. For example, an infection in your airways causes the common cold. And an infection in your skin can cause rashes such as athlete's foot.

infection.

Your lungs keep you from getting infections in several ways.

The airways in your lungs are lined with tiny hairs. These are covered with a sticky substance that traps harmful germs and particles. These hairs wave back and forth. This pushes harmful things out of your lungs.

Source:
Levison ME.
Pneumonia, including necrotizing pulmonary infections (lung abscess)
In: Braunwald E, Hauser SL, Fauci AS, et al. Harrison's principles of internal medicine. 15th edition. McGraw Hill, New York, U.S.A.; 2001.

²
Further down in the lungs there are special cells that fight any infection that has made it past the first hurdle (the tiny hairs).
Coughing is another way your lungs get rid of harmful things. Coughing happens without you thinking about it. It is your body's way of trying to clear things out of your airways that might irritate them. This type of automatic action is called a reflex action.

What happens when you get pneumonia?

You get pneumonia when harmful germs get past your lungs' defense systems and start to multiply. This causes an infection. Often, these germs are already in your nose and throat. Sometimes they are in tiny drops in the air (for example, after someone sneezes), and you breathe them in. You can get an infection in just one of your lungs or in both of them.

If an infection gets into your lungs, your lungs become

inflammation
If your skin or some other part of your body becomes red, swollen, hot or sore, we say it is inflamed. It means that your body is trying to protect you from germs, from something in your body tissues that can hurt you (like a thorn or sliver), or from things that cause allergies (allergens). Inflammation is part of the way the body heals an infection or injury.

inflamed. This is one of the ways that your body tries to fight an infection. What happens is that special chemicals are released by your body's cells. And this makes more blood flow to the infected area. Along with the blood, infection-fighting parts of the

immune system
The immune system is made up of the parts of the body that are devoted to fighting infection. The body is constantly being threatened by infections from things like bacteria, viruses and parasites. The immune system fights these infections in different ways. At the microscopic level, the immune system uses antibodies and white blood cells, which travel in the blood and target infectious agents, such as bacteria. These microscopic parts of the immune system either kill the infectious agent directly, or take it to other parts of the body, like the spleen, where it can be dealt with. The lymph nodes are another important part of the immune system. Within them, white blood cells filter through the foreign material that has entered the blood, to see if there are any infections. When you have a swollen gland during a cold, this is actually a lymph node that is reacting to the infection. Unfortunately, it is possible for the immune system to become confused and to use its destructive powers to target healthy parts of the body. Diseases that result from this type of situation are called autoimmune diseases.

immune system also travel through your body to the site of the infection.

An X-ray showing normal lungs.

An X-ray showing pneumonia.

Even though inflammation is one of the ways that your body responds to an infection or an injury, it can cause other problems in your body. In the case of pneumonia, it irritates your airways and makes your lungs heavy and stiff because of the extra blood. This is why you have trouble catching your breath. Also, fluid made by the inflamed tissue builds up in the tiny air sacs at the end of your airways. And this makes it difficult for oxygen to come into your body and for carbon dioxide to leave.

Meanwhile, your immune system (which protects your body against invading germs) responds to the infection that has gotten into your lungs. For example, cells in your blood (called

white blood cells
White blood cells are the cells in your blood that help your body fight infections. The other cells in your blood, red blood cells, carry oxygen around your body.

white blood cells) are an important part of your body's defense system. If you have an infection, the white blood cells travel to that area, where they surround the invading germs and destroy them.

If you have a serious infection, such as pneumonia, a blood test may show that you have more white cells than normal in your blood. This is often a sign that your body is working to fight off the infection.

Source:
Guyton AC, Hall JE
Resistance of the body to infection: I. Leukocytes, granulocytes, the monocyte-macrophage system, and inflammation.
In: Textbook of medical physiology. WB Saunders, Philadelphia, U.S.A.; 2000.

What causes pneumonia?

In most cases of pneumonia, the germs that cause it are

bacteria
Bacteria are tiny organisms. There are lots of different types. Some are harmful and can cause disease. But some bacteria live in your body without causing any harm.

bacteria. But pneumonia can also be caused by

viruses
Viruses are microbes (tiny organisms) that need the cells of humans or other animals to exist. They use the machinery of cells to reproduce. Then they spread to other cells in the body.

viruses. In rare cases, pneumonia is caused by another type of germ called a

fungus
A fungus is an organism that is sometimes considered to be a type of plant. A fungus lives by feeding on other organisms. The mushrooms we eat in salads are fungi, but so are candida and cryptococcus, which can cause infections in people's bodies.

fungus. Sometimes pneumonia is caused by two different germs (bacteria and a virus).

Different types of germs cause different types of symptoms. Some germs may make you more ill than others. In about one-third of cases, doctors can't tell what type of germ caused the pneumonia.

The most common form of pneumonia is pneumococcal pneumonia. Pneumococci are bacteria. About half of all cases of pneumonia are caused by pneumococci.

Source:
Bartlett JG, Mundy LM.
Community-acquired pneumonia.
New England Journal of Medicine. 1995; 333: 1618-1624.

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To learn more, see Germs that cause pneumonia.

There are vaccines that can help keep you from getting pneumococcal pneumonia. A vaccine is usually given as a shot and keeps you from getting a specific disease. The vaccine may make it less likely that you'll get pneumococcal pneumonia, but it won't help if you already have it. The vaccine may also keep you from getting some of the more severe complications of pneumonia.

To learn more, see Vaccines that help protect you against pneumonia.

Is it easy to catch pneumonia?

If you're healthy, you probably won't catch pneumonia from someone else. But people often have small amounts of some of the germs that cause pneumonia in their nose and throat. And these can be passed on when someone sneezes or coughs or has other close contact, such as hugging or kissing. If you are older or already have a serious illness, these germs may get into your lungs and cause pneumonia. Some types of pneumonia are contagious, such as pneumonia caused by the

flu
The flu is a bad infection that gives you a headache, sore throat, aching joints and a fever. Flu is caused by infection with a virus called influenza.

flu virus.

If you have pneumonia, there are some things you can do to keep from spreading it around. You should:

Cover your mouth and nose when you cough or sneeze
Throw out your used tissues. Don't leave them lying around
Wash your hands regularly and well
Avoid contact with anyone who has an increased risk of getting pneumonia. This could be someone whose immune system has been weakened by

chemotherapy
Chemotherapy is the use of chemicals or drugs to treat or prevent disease, usually cancer.

chemotherapy or

AIDS
AIDS stands for acquired immunodeficiency syndrome. People who are infected with the human immunodeficiency virus (HIV) get AIDS when the virus has destroyed most of their immune system. When people have AIDS, their body isn't able to fight infections. So even common infections, such as colds, can cause serious problems.

HIV or AIDS, or an elderly person.

Am I at risk of getting pneumonia?

Some people are more likely to get pneumonia than others. Doctors call the things that increase your risk for a disease risk factors. Having a risk factor doesn't mean you'll get pneumonia for sure. It just means you're more likely to get it than someone who doesn't have the risk factor.

You should be especially aware of the dangers of pneumonia if you or someone in your family:

Is over 65 years old
Is under the age of 2 years old
Is a heavy smoker (smoking damages your lungs, so you're more likely to get an infection)
Is a heavy drinker
Already has a lung disease, such as

asthma
Asthma is a long-term disease of the lungs. It makes you wheeze, cough and feel short of breath. Asthma attacks are caused by iflammation and narrowing of the airways, which makes it hard for air to pass in and out of the lungs.

asthma or

emphysema
Emphysema is a long-term disease of the lungs. The walls of the air sacs (alveoli) in the lungs become thin and less elastic. This makes it harder for oxygen to get in your blood and carbon dioxide to get out of your body. It makes you cough and feel short of breath. Smoking is the most common cause of emphysema.

emphysema
Has recently had another illness, such as the flu, which could have weakened their immune system
Has a long-term (chronic) disease, such as

diabetes
Diabetes is a condition that causes too much sugar to circulate in your blood. It happens when your body stops making a hormone called insulin (type 1 diabetes) or when insulin stops working (type 2 diabetes).

diabetes,

heart disease
You get heart disease when your heart isn't able to pump blood as well as it should. This can happen for a variety of reasons.

heart disease or

sickle cell disease
Sickle cell disease is a blood disorder that runs in families. Under certain conditions, the red blood cells of people with this disease change shape to look like a sickle. This causes a lot of pain and a range of other symptoms, including infections in the lungs.

sickle cell disease
Has

AIDS
AIDS stands for acquired immunodeficiency syndrome. People who are infected with the human immunodeficiency virus (HIV) get AIDS when the virus has destroyed most of their immune system. When people have AIDS, their body isn't able to fight infections. So even common infections, such as colds, can cause serious problems.

AIDS, or

leukemia
Leukemia is a type of cancer that affects the body's production of white blood cells. White blood cells are important for fighting infections. So, if you have leukemia you are more likely to catch an infectious disease.

leukemia or another type of cancer
Takes medicine for an illness such as

AIDS
AIDS stands for acquired immunodeficiency syndrome. People who are infected with the human immunodeficiency virus (HIV) get AIDS when the virus has destroyed most of their immune system. When people have AIDS, their body isn't able to fight infections. So even common infections, such as colds, can cause serious problems.

AIDS or cancer (some medicines can make it harder for your body to fight off an infection, such as those given for

chemotherapy
Chemotherapy is the use of chemicals or drugs to treat or prevent disease, usually cancer.

chemotherapy)
Has had an organ transplant.

All these things affect your body's natural ability to fight off infections. This is why they put you at a higher risk for pneumonia.

If you fall into any of these groups, you can take steps to protect yourself from pneumonia. You can take extra care and look after yourself. And you may also want to consider being vaccinated.

For more, see Vaccines that help protect you against pneumonia.

Sources for the information on this page:

National Heart, Lung and Blood InstituteThe lungs in health and diseaseNIH Publication No. 97-3279

Levison ME.Pneumonia, including necrotizing pulmonary infections (lung abscess)In: Braunwald E, Hauser SL, Fauci AS, et al. Harrison's principles of internal medicine. 15th edition. McGraw Hill, New York, U.S.A.; 2001.

Guyton AC, Hall JEResistance of the body to infection: I. Leukocytes, granulocytes, the monocyte-macrophage system, and inflammation.In: Textbook of medical physiology. WB Saunders, Philadelphia, U.S.A.; 2000.

Bartlett JG, Mundy LM.Community-acquired pneumonia.New England Journal of Medicine. 1995; 333: 1618-1624.

This information was last updated on Jan 07, 2009

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© BMJ Publishing Group Limited 2009. All rights reserved.

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