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What Is Pneumonia?

Pneumonia (nu-MO-ne-ah) is an infection in one or both of the lungs. Many germs—such as bacteria, viruses, and fungi—can cause pneumonia.

The infection inflames your lungs' air sacs, which are called alveoli (al-VEE-uhl-eye). The air sacs may fill up with fluid or pus, causing symptoms such as a cough with phlegm (a slimy substance), fever, chills, and trouble breathing.


Pneumonia and its symptoms can vary from mild to severe. Many factors affect how serious pneumonia is, such as the type of germ causing the infection and your age and overall health.

Pneumonia tends to be more serious for:

  • Infants and young children.
  • Older adults (people 65 years or older).
  • People who have other health problems, such as heart failure, diabetes, or COPD (chronic obstructive pulmonary disease).
  • People who have weak immune systems as a result of diseases or other factors. Examples of these diseases and factors include HIV/AIDS, chemotherapy (a treatment for cancer), and an organ transplant or blood and marrow stem cell transplant.


Pneumonia is common in the United States. Treatment for pneumonia depends on its cause, how severe your symptoms are, and your age and overall health. Many people can be treated at home, often with oral antibiotics.

Children usually start to feel better in 1 to 2 days. For adults, it usually takes 2 to 3 days. Anyone who has worsening symptoms should see a doctor.

People who have severe symptoms or underlying health problems may need treatment in a hospital. It may take 3 weeks or more before they can go back to their normal routines.

Fatigue (tiredness) from pneumonia can last for a month or more.

Types of Pneumonia

Pneumonia is named for the way in which a person gets the infection or for the germ that causes it.

Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) occurs outside of hospitals and other health care settings. Most people get CAP by breathing in germs (especially while sleeping) that live in the mouth, nose, or throat.

CAP is the most common type of pneumonia. Most cases occur during the winter. About 4 million people get this form of pneumonia each year. About 1 out of every 5 people who has CAP needs to be treated in a hospital.

Hospital-Acquired Pneumonia

Some people catch pneumonia during a hospital stay for another illness. This is called hospital-acquired pneumonia (HAP). You're at higher risk of getting HAP if you're on a ventilator (a machine that helps you breathe).

HAP tends to be more serious than CAP because you're already sick. Also, hospitals tend to have more germs that are resistant to antibiotics (medicines used to treat pneumonia).

Health Care-Associated Pneumonia

Patients also may get pneumonia in other health care settings, such as nursing homes, dialysis centers, and outpatient clinics. This type of pneumonia is called health care-associated pneumonia.

Other Common Types of Pneumonia

Aspiration Pneumonia

This type of pneumonia can occur if you inhale food, drink, vomit, or saliva from your mouth into your lungs. This may happen if something disturbs your normal gag reflex, such as a brain injury, swallowing problem, or excessive use of alcohol or drugs.

Aspiration pneumonia can cause pus to form in a cavity in the lung. When this happens, it's called a lung abscess (AB-ses).

Atypical Pneumonia

Several types of bacteria—Legionella pneumophila, mycoplasma pneumonia, and Chlamydophila pneumoniae—cause atypical pneumonia, a type of CAP. Atypical pneumonia is passed from person to person.

Other Names for Pneumonia

  • Pneumonitis (nu-mo-NI-tis).
  • Bronchopneumonia (BRONG-ko-nu-MO-ne-ah).
  • Nosocomial (nos-o-KO-me-al) pneumonia. This is another name for hospital-acquired pneumonia.
  • Walking pneumonia. This refers to pneumonia that's mild enough that you're not bedridden.
  • Double pneumonia. This refers to pneumonia that affects both lobes of the lungs.

What Causes Pneumonia?

Many germs can cause pneumonia. Examples include different kinds of bacteria, viruses, and, less often, fungi.

Most of the time, the body filters germs out of the air that we breathe to protect the lungs from infection. Your immune system, the shape of your nose and throat, your ability to cough, and fine, hair-like structures called cilia (SIL-e-ah) help stop the germs from reaching your lungs. (For more information, go to the Health Topics How the Lungs Work article.)

Sometimes, though, germs manage to enter the lungs and cause infections. This is more likely to occur if:

  • Your immune system is weak
  • A germ is very strong
  • Your body fails to filter germs out of the air that you breathe

For example, if you can't cough because you've had a stroke or are sedated, germs may remain in your airways. ("Sedated" means you're given medicine to make you sleepy.)

When germs reach your lungs, your immune system goes into action. It sends many kinds of cells to attack the germs. These cells cause the alveoli (air sacs) to become red and inflamed and to fill up with fluid and pus. This causes the symptoms of pneumonia.

Germs That Can Cause Pneumonia


Bacteria are the most common cause of pneumonia in adults. Some people, especially the elderly and those who are disabled, may get bacterial pneumonia after having the flu or even a common cold.

Many types of bacteria can cause pneumonia. Bacterial pneumonia can occur on its own or develop after you've had a cold or the flu. This type of pneumonia often affects one lobe, or area, of a lung. When this happens, the condition is called lobar pneumonia.

The most common cause of pneumonia in the United States is the bacterium Streptococcus (strep-to-KOK-us) pneumoniae, or pneumococcus (nu-mo-KOK-us).

Lobar Pneumonia

Figure A shows the location of the lungs and airways in the body. This figure also shows pneumonia that's affecting the lower lobe of the left lung. Figure B shows normal alveoli. Figure C shows infected alveoli.

Figure A shows the location of the lungs and airways in the body. This figure also shows pneumonia affecting the lower lobe of the left lung. Figure B shows normal alveoli. Figure C shows infected alveoli.

Another type of bacterial pneumonia is called atypical pneumonia. Atypical pneumonia includes:

  • Legionella pneumophila. This type of pneumonia sometimes is called Legionnaire's disease, and it has caused serious outbreaks. Outbreaks have been linked to exposure to cooling towers, whirlpool spas, and decorative fountains.
  • Mycoplasma pneumonia. This is a common type of pneumonia that usually affects people younger than 40 years old. People who live or work in crowded places like schools, homeless shelters, and prisons are at higher risk for this type of pneumonia. It's usually mild and responds well to treatment with antibiotics. However, mycoplasma pneumonia can be very serious. It may be associated with a skin rash and hemolysis (the breakdown of red blood cells).
  • Chlamydophila pneumoniae. This type of pneumonia can occur all year and often is mild. The infection is most common in people 65 to 79 years old.


Respiratory viruses cause up to one-third of the pneumonia cases in the United States each year. These viruses are the most common cause of pneumonia in children younger than 5 years old.

Most cases of viral pneumonia are mild. They get better in about 1 to 3 weeks without treatment. Some cases are more serious and may require treatment in a hospital.

If you have viral pneumonia, you run the risk of getting bacterial pneumonia as well.

The flu virus is the most common cause of viral pneumonia in adults. Other viruses that cause pneumonia include respiratory syncytial virus, rhinovirus, herpes simplex virus, severe acute respiratory syndrome (SARS), and more.


Three types of fungi in the soil in some parts of the United States can cause pneumonia. These fungi are:

  • Coccidioidomycosis (kok-sid-e-OY-do-mi-KO-sis). This fungus is found in Southern California and the desert Southwest.
  • Histoplasmosis (HIS-to-plaz-MO-sis). This fungus is found in the Ohio and Mississippi River Valleys.
  • Cryptococcus (krip-to-KOK-us). This fungus is found throughout the United States in bird droppings and soil contaminated with bird droppings.

Most people exposed to these fungi don't get sick, but some do and require treatment.

Serious fungal infections are most common in people who have weak immune systems due to the long-term use of medicines to suppress their immune systems or having HIV/AIDS.

Pneumocystis jiroveci (nu-mo-SIS-tis ye-RO-VECH-e), formerly Pneumocystis carinii, sometimes is considered a fungal pneumonia. However, it's not treated with the usual antifungal medicines. This type of infection is most common in people who:

Other kinds of fungal infections also can lead to pneumonia.

Who Is at Risk for Pneumonia?

Pneumonia can affect people of all ages. However, two age groups are at greater risk of developing pneumonia:

  • Infants who are 2 years old or younger (because their immune systems are still developing during the first few years of life)
  • People who are 65 years old or older

Other conditions and factors also raise your risk for pneumonia. You're more likely to get pneumonia if you have a lung disease or other serious disease. Examples include cystic fibrosis, asthma, COPD (chronic obstructive pulmonary disease), bronchiectasis, diabetes, heart failure, and sickle cell anemia.

You're at greater risk for pneumonia if you're in a hospital intensive-care unit, especially if you're on a ventilator (a machine that helps you breathe).

Having a weak or suppressed immune system also raises your risk for pneumonia. A weak immune system may be the result of a disease such as HIV/AIDS. A suppressed immune system may be due to an organ transplant or blood and marrow stem cell transplant, chemotherapy (a treatment for cancer), or long-term steroid use.

Your risk for pneumonia also increases if you have trouble coughing because of a stroke or problems swallowing. You're also at higher risk if you can't move around much or are sedated (given medicine to make you relaxed or sleepy).

Smoking cigarettes, abusing alcohol, or being undernourished also raises your risk for pneumonia. Your risk also goes up if you've recently had a cold or the flu, or if you're exposed to certain chemicals, pollutants, or toxic fumes.

What Are the Signs and Symptoms of Pneumonia?

The signs and symptoms of pneumonia vary from mild to severe. Many factors affect how serious pneumonia is, including the type of germ causing the infection and your age and overall health. (For more information, go to "Who Is at Risk for Pneumonia?")

See your doctor promptly if you:

  • Have a high fever
  • Have shaking chills
  • Have a cough with phlegm (a slimy substance), which doesn't improve or worsens
  • Develop shortness of breath with normal daily activities
  • Have chest pain when you breathe or cough
  • Feel suddenly worse after a cold or the flu

People who have pneumonia may have other symptoms, including nausea (feeling sick to the stomach), vomiting, and diarrhea.

Symptoms may vary in certain populations. Newborns and infants may not show any signs of the infection. Or, they may vomit, have a fever and cough, or appear restless, sick, or tired and without energy.

Older adults and people who have serious illnesses or weak immune systems may have fewer and milder symptoms. They may even have a lower than normal temperature. If they already have a lung disease, it may get worse. Older adults who have pneumonia sometimes have sudden changes in mental awareness.

Complications of Pneumonia

Often, people who have pneumonia can be successfully treated and not have complications. But some people, especially those in high-risk groups, may have complications such as:

  • Bacteremia (bak-ter-E-me-ah). This serious complication occurs if the infection moves into your bloodstream. From there, it can quickly spread to other organs, including your brain.
  • Lung abscesses. An abscess occurs if pus forms in a cavity in the lung. An abscess usually is treated with antibiotics. Sometimes surgery or drainage with a needle is needed to remove the pus.
  • Pleural effusion. Pneumonia may cause fluid to build up in the pleural space. This is a very thin space between two layers of tissue that line the lungs and the chest cavity. Pneumonia can cause the fluid to become infected—a condition called empyema (em-pi-E-ma). If this happens, you may need to have the fluid drained through a chest tube or removed with surgery.

How Is Pneumonia Diagnosed?

Pneumonia can be hard to diagnose because it may seem like a cold or the flu. You may not realize it's more serious until it lasts longer than these other conditions.

Your doctor will diagnose pneumonia based on your medical history, a physical exam, and test results.

Medical History

Your doctor will ask about your signs and symptoms and how and when they began. To find out what type of germ is causing the pneumonia, he or she also may ask about:

  • Any recent traveling you've done
  • Your hobbies
  • Your exposure to animals
  • Your exposure to sick people at home, school, or work
  • Your past and current medical conditions, and whether any have gotten worse recently
  • Any medicines you take
  • Whether you smoke
  • Whether you've had flu or pneumonia vaccinations

Physical Exam

Your doctor will listen to your lungs with a stethoscope. If you have pneumonia, your lungs may make crackling, bubbling, and rumbling sounds when you inhale. Your doctor also may hear wheezing.

Your doctor may find it hard to hear sounds of breathing in some areas of your chest.

Diagnostic Tests

If your doctor thinks you have pneumonia, he or she may recommend one or more of the following tests.

Chest X Ray

A chest x ray is a painless test that creates pictures of the structures inside your chest, such as your heart, lungs, and blood vessels.

A chest x ray is the best test for diagnosing pneumonia. However, this test won't tell your doctor what kind of germ is causing the pneumonia.

Blood Tests

Blood tests involve taking a sample of blood from a vein in your body. A complete blood count (CBC) measures many parts of your blood, including the number of white blood cells in the blood sample. The number of white blood cells can show whether you have a bacterial infection.

Your doctor also may recommend a blood culture to find out whether the infection has spread to your bloodstream. This test is used to detect germs in the bloodstream. A blood culture may show which germ caused the infection. If so, your doctor can decide how to treat the infection.

Other Tests

Your doctor may recommend other tests if you're in the hospital, have serious symptoms, are older, or have other health problems.

Sputum test. Your doctor may look at a sample of sputum (spit) collected from you after a deep cough. This may help your doctor find out what germ is causing your pneumonia. Then, he or she can plan treatment.

Chest computed tomography (CT) scan. A chest CT scan is a painless test that creates precise pictures of the structures in your chest, such as your lungs. A chest CT scan is a type of x ray, but its pictures show more detail than those of a standard chest x ray.

Pleural fluid culture. For this test, a fluid sample is taken from the pleural space (a thin space between two layers of tissue that line the lungs and chest cavity). Doctors use a procedure called thoracentesis (THOR-ah-sen-TE-sis) to collect the fluid sample. The fluid is studied for germs that may cause pneumonia.

Pulse oximetry. For this test, a small sensor is attached to your finger or ear. The sensor uses light to estimate how much oxygen is in your blood. Pneumonia can keep your lungs from moving enough oxygen into your bloodstream.

If you're very sick, your doctor may need to measure the level of oxygen in your blood using a blood sample. The sample is taken from an artery, usually in your wrist. This test is called an arterial blood gas test.

Bronchoscopy. Bronchoscopy (bron-KOS-ko-pee) is a procedure used to look inside the lungs' airways. If you're in the hospital and treatment with antibiotics isn't working well, your doctor may use this procedure.

Your doctor passes a thin, flexible tube through your nose or mouth, down your throat, and into the airways. The tube has a light and small camera that allow your doctor to see your windpipe and airways and take pictures.

Your doctor can see whether something is blocking your airways or whether another factor is contributing to your pneumonia.

How Is Pneumonia Treated?

Treatment for pneumonia depends on the type of pneumonia you have and how severe it is. Most people who have community-acquired pneumonia—the most common type of pneumonia—are treated at home.

The goals of treatment are to cure the infection and prevent complications.

General Treatment

If you have pneumonia, follow your treatment plan, take all medicines as prescribed, and get ongoing medical care. Ask your doctor when you should schedule followup care. Your doctor may want you to have a chest x ray to make sure the pneumonia is gone.

Although you may start feeling better after a few days or weeks, fatigue (tiredness) can persist for up to a month or more. People who are treated in the hospital may need at least 3 weeks before they can go back to their normal routines.

Bacterial Pneumonia

Bacterial pneumonia is treated with medicines called antibiotics. You should take antibiotics as your doctor prescribes. You may start to feel better before you finish the medicine, but you should continue taking it as prescribed. If you stop too soon, the pneumonia may come back.

Most people begin to improve after 1 to 3 days of antibiotic treatment. This means that they should feel better and have fewer symptoms, such as cough and fever.

Viral Pneumonia

Antibiotics don't work when the cause of pneumonia is a virus. If you have viral pneumonia, your doctor may prescribe an antiviral medicine to treat it.

Viral pneumonia usually improves in 1 to 3 weeks.

Treating Severe Symptoms

You may need to be treated in a hospital if:

  • Your symptoms are severe
  • You're at risk for complications because of other health problems

If the level of oxygen in your bloodstream is low, you may receive oxygen therapy. If you have bacterial pneumonia, your doctor may give you antibiotics through an intravenous (IV) line inserted into a vein.

How Can Pneumonia Be Prevented?

Pneumonia can be very serious and even life threatening. When possible, take steps to prevent the infection, especially if you're in a high-risk group.


Vaccines are available to prevent pneumococcal pneumonia and the flu. Vaccines can't prevent all cases of infection. However, compared to people who don't get vaccinated, those who do and still get pneumonia tend to have:

  • Milder cases of the infection
  • Pneumonia that doesn't last as long
  • Fewer serious complications

Pneumococcal Pneumonia Vaccine

A vaccine is available to prevent pneumococcal pneumonia. In most adults, one shot is good for at least 5 years of protection. This vaccine often is recommended for:

  • People who are 65 years old or older.
  • People who have chronic (ongoing) diseases, serious long-term health problems, or weak immune systems. For example, this may include people who have cancer, HIV/AIDS, asthma, or damaged or removed spleens.
  • People who smoke.
  • Children who are younger than 5 years old.
  • Children who are 5–18 years of age with certain medical conditions, such as heart or lung diseases or cancer. For more information, talk with your child's doctor.

For more information about the pneumococcal pneumonia vaccine, go to the Centers for Disease Control and Prevention's (CDC's) Vaccines and Preventable Diseases: Pneumococcal Vaccination Web page.

Influenza Vaccine

The vaccine that helps prevent the flu is good for 1 year. It's usually given in October or November, before peak flu season.

Because many people get pneumonia after having the flu, this vaccine also helps prevent pneumonia.

For more information about the influenza vaccine, go to the CDC's Vaccines and Preventable Diseases: Seasonal Influenza (Flu) Vaccination Web page.

Hib Vaccine

Haemophilus influenzae type b (Hib) is a type of bacteria that can cause pneumonia and meningitis (men-in-JI-tis). (Meningitis is an infection of the covering of the brain and spinal cord.) The Hib vaccine is given to children to help prevent these infections.

The vaccine is recommended for all children in the United States who are younger than 5 years old. The vaccine often is given to infants starting at 2 months of age.

For more information about the Hib vaccine, go to the CDC's Vaccines and Preventable Diseases: Hib Vaccination Web page.

Other Ways To Help Prevent Pneumonia

You also can take the following steps to help prevent pneumonia:

  • Wash your hands with soap and water or alcohol-based rubs to kill germs.
  • Don't smoke. Smoking damages your lungs' ability to filter out and defend against germs. For information about how to quit smoking, go to the Health Topics Smoking and Your Heart article. Although this resource focuses on heart health, it includes general information about how to quit smoking.
  • Keep your immune system strong. Get plenty of rest and physical activity and follow a healthy diet.

If you have pneumonia, limit contact with family and friends. Cover your nose and mouth while coughing or sneezing, and get rid of used tissues right away. These actions help keep the infection from spreading.

Living With Pneumonia

If you have pneumonia, you can take steps to recover from the infection and prevent complications.

  • Get plenty of rest.
  • Follow your treatment plan as your doctor advises.
  • Take all medicines as your doctor prescribes. If you're using antibiotics, continue to take the medicine until it's all gone. You may start to feel better before you finish the medicine, but you should continue to take it. If you stop too soon, the pneumonia may come back.
  • Ask your doctor when you should schedule followup care. Your doctor may recommend a chest x ray to make sure the infection is gone.

It may take time to recover from pneumonia. Some people feel better and are able to return to their normal routines within a week. For other people, it can take a month or more. Most people continue to feel tired for about a month. Talk with your doctor about when you can go back to your normal routine.

Clinical Trials

The National Heart, Lung, and Blood Institute (NHLBI) is strongly committed to supporting research aimed at preventing and treating heart, lung, and blood diseases and conditions and sleep disorders.

NHLBI-supported research has led to many advances in medical knowledge and care. Often, these advances depend on the willingness of volunteers to take part in clinical trials.

Clinical trials test new ways to prevent, diagnose, or treat various diseases and conditions. For example, new treatments for a disease or condition (such as medicines, medical devices, surgeries, or procedures) are tested in volunteers who have the illness. Testing shows whether a treatment is safe and effective in humans before it is made available for widespread use.

By taking part in a clinical trial, you can gain access to new treatments before they're widely available. You also will have the support of a team of health care providers, who will likely monitor your health closely. Even if you don't directly benefit from the results of a clinical trial, the information gathered can help others and add to scientific knowledge.

If you volunteer for a clinical trial, the research will be explained to you in detail. You'll learn about treatments and tests you may receive, and the benefits and risks they may pose. You'll also be given a chance to ask questions about the research. This process is called informed consent.

If you agree to take part in the trial, you'll be asked to sign an informed consent form. This form is not a contract. You have the right to withdraw from a study at any time, for any reason. Also, you have the right to learn about new risks or findings that emerge during the trial.

For more information about clinical trials related to pneumonia, talk with your doctor. You also can visit the following Web sites to learn more about clinical research and to search for clinical trials:

For more information about clinical trials for children, visit the NHLBI's Children and Clinical Studies Web page.

Links to Other Information About Pneumonia

NHLBI Resources

Non-NHLBI Resources

Clinical Trials

March 01, 2011 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.