What Is Pneumonia?

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

The infection causes your lungs’ air sacs, called alveoli (al-VEE-uhl-eye), to become inflamed. The air sacs may fill up with fluid or pus, causing symptoms such as a cough (with phlegm), fever, chills, and trouble breathing.

Overview

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 like heart failure, diabetes, or COPD (chronic obstructive pulmonary disease).
• People who have weak immune systems as a result of diseases or other factors. These may include HIV/AIDS, chemotherapy (a treatment for cancer), or an organ or bone marrow transplant.

Outlook

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 whose symptoms get worse should be checked by a doctor.

People who have more 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 for getting HAP if you’re on a mechanical ventilator (a machine that helps you breathe).

HAP tends to be more serious than CAP. This is because you’re already sick. Also, hospitals tend to have more germs that are resistant to antibiotics—a treatment for 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 is called health care-associated pneumonia.

Other Common Types of Pneumonia

Aspiration Pneumonia

This type of pneumonia occurs when you accidentally inhale food, drink, vomit, or saliva from your mouth into your lungs. This usually happens when 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. This is called a lung abscess.

Atypical Pneumonia

Several types of bacteria—Legionella pneumophila, mycoplasma pneumonia, and Chlamydophila pneumoniae—cause this 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 different germs can cause pneumonia. These 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. (For more information, see the Diseases and Conditions Index “How the Lungs Work” article.) Sometimes, though, germs manage to enter the lungs and cause infections. This is more likely to occur when:

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

Your mouth and airways are exposed to germs as you inhale air through your nose and mouth. 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 example, coughing is one way the body keeps germs from reaching the lungs. Some people may not be able to cough because, for example, they’ve had a stroke or are sedated (given medicine to make them sleepy). This means germs may remain in the airways rather than being coughed out.

When germs do 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

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.

Dozens of different 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. It also shows pneumonia that’s 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 is sometimes called Legionnaire's disease. This type of pneumonia 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. People who live or work in crowded places like schools, homeless shelters, and prisons are most likely to get it. It’s usually mild and responds well to treatment with antibiotics. But, it can be very serious in some people. It may be associated with a skin rash and hemolysis (the breakdown of red blood cells).
• Chlamydophila pneumoniae. This kind of pneumonia can occur all year and is often mild. The infection is most common in people 65 to 79 years of age.

Viruses

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.

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 also.

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.

Fungi

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) in Southern California and the desert Southwest, histoplasmosis (HIS-to-plaz-MO-sis) in the Ohio and Mississippi River Valleys, and cryptococcus (krip-to-KOK-us). 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 as a result of long-term use of medicines to suppress their immune systems or having HIV/AIDS.

Pneumocystis jirovecii (nu-mo-SIS-tis ye-RO-VECH-e), formerly Pneumocystis carinii, is sometimes considered a fungal pneumonia. However, it’s not treated with the usual antifungal medicines. It usually affects people who:

• Have HIV/AIDS or cancer
• Have had an organ and/or bone marrow transplant
• Take medicines that affect their immune systems

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 or younger, because their immune systems are still developing during the first few years of life
• People who are 65 years 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 to help you breathe).

Having a weak or suppressed immune system also can raise your risk. 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 or bone marrow transplant, chemotherapy (treatment for cancer), or long-term steroid use.

Your risk also goes up if you have trouble coughing because of a stroke, trouble swallowing, limited ability to move, alcohol use, or sedation (being given medicine to make you relaxed or sleepy).

Smoking cigarettes, abusing alcohol, and being undernourished also raise 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 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, see “Who Is At Risk for Pneumonia?” )

See your doctor promptly if you:

• Have a high fever
• Have shaking chills
• Have a cough with phlegm, 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 with pneumonia may have other symptoms, including nausea (feeling sick to your stomach), vomiting, and diarrhea.

Symptoms may vary in certain populations. Newborns and infants may not show any signs of the infection or 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 treated successfully and not have complications. But some patients, especially those in high-risk groups, may have complications such as:

• Bacteremia (bak-ter-E-me-ah). This serious complication occurs when the infection moves into your bloodstream. From there, it can quickly spread to other organs, including your brain.
• Lung abscess. An abscess occurs when pus forms in a cavity in the lung. An abscess usually is treated with antibiotics. In some cases, surgery or needle drainage is needed to remove it.
• Pleural effusion. Pneumonia may cause fluid to build up in the pleural space, which is the space between your lungs and chest wall. 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 through surgery.

How Is Pneumonia Diagnosed?

Pneumonia can be hard to diagnose because it may seem like a cold or the flu. People 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 and the results from a physical exam and tests.

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 a flu or pneumonia vaccination

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. It may be hard to hear sounds of breathing in some areas of your chest. Your doctor also may hear wheezing.

Diagnostic Tests

If your doctor suspects you have pneumonia, he or she also may order 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 and lungs.

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

Other Tests

You may need 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 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 kind of x ray, but its pictures show more detail than those of a standard chest x ray.

Pleural fluid culture. For this test, a sample of fluid is taken from the space between your lungs and chest wall (the pleural space). This is done using a procedure called thoracentesis (THOR-a-sen-TE-sis). The fluid is studied for germs that may cause pneumonia.

Pulse oximetry. For this test, a small clip is attached to your finger or ear to show 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.

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 test.

Your doctor passes a thin, flexible tube with a camera on its tip through your nose or mouth, down your throat, and into the airways.

This test allows your doctor to 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

It’s important to follow your treatment plan, take all medicines as prescribed, and get ongoing medical care. Talk to your doctor about 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 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

Viral pneumonia isn’t treated with antibiotics. This type of medicine doesn’t work when a virus causes the pneumonia. 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. 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

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 people, one shot is good for at least 5 years of protection. This vaccine is often recommended for:

• People who are 65 years or older.
• People who have chronic diseases, serious long-term health problems, or weak immune systems. Examples include people who have cancer, HIV/AIDS, or damaged or removed spleens.
• Alaska Natives and certain American Indian populations.
• Children who are 2 years or younger, and children between the ages of 2 and 5 who have a chronic disease (like cancer or HIV/AIDS) or are Alaska Natives, American Indians, or African Americans. The vaccine also is recommended for children between the ages of 2 and 5 who attend group daycare programs.

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.

Hib Vaccine

Haemophilus influenzae type b (Hib) is a type of bacteria that can cause pneumonia and meningitis (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. It’s often given to infants starting at 2 months of age.

Other Ways To Help Prevent Pneumonia

Other steps also can 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.
• 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 dispose of tissues right away. These measures 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 the treatment plan your doctor gives you.
• 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.
• Talk to your doctor about when to schedule followup care. Your doctor may order 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 to your doctor about when you can go back to your normal activities.

Key Points

• Pneumonia is an infection in one or both of your lungs. Many small germs, such as bacteria, viruses, and fungi, can cause pneumonia.
• The infection causes your lungs’ air sacs, called alveoli, to become inflamed. The air sacs may fill up with fluid or pus, causing symptoms such as a cough (with phlegm), fever, chills, and trouble breathing.
• Pneumonia and its symptoms can 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.
• Pneumonia tends to be more serious for infants and young children, older adults (people 65 years or older), people who have other chronic health problems, and people who have weak immune systems as a result of diseases or other factors.
• Your doctor will diagnose pneumonia based on your medical history and the results from a physical exam and tests.
• Treatment for pneumonia depends on its cause, how severe your symptoms are, and your age and overall health. The goals of treatment are to cure the infection and prevent complications. People who have more severe symptoms or underlying health problems may need treatment in the hospital.
• Pneumonia can be very serious and even life threatening. When possible, take steps to prevent the infection. Vaccines are available to prevent pneumococcal pneumonia and the flu. Other steps also can 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.
  • 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 dispose of tissues right away. Follow the treatment plan your doctor gives you and get plenty of rest.
• 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. Talk to your doctor about when you can go back to your normal routine.

Links to Other Information About Pneumonia

NHLBI Resources

• How the Lungs Work (Diseases and Conditions Index)

Non-NHLBI Resources

• Pneumonia (MedlinePlus)

Clinical Trials

• Current Research (ClinicalTrials.gov)