Pneumonia

Definition

Pneumonia is an infection that affects one or both lungs. It causes the air sacs, or alveoli, of the lungs to fill up with fluid or pus. Bacteria, viruses, or fungi may cause pneumonia. Symptoms can range from mild to serious and may include a cough with or without mucus (a slimy substance), fever, chills, and trouble breathing. How serious your pneumonia is depends on your age, your overall health, and what caused your infection.

Influenza/pneumonia mortality is one of the leading causes of death in the United States and shows persistent racial disparities in the biggest cities disproportionately affect people of color.

Symptoms

The symptoms of pneumonia can be mild or serious. Young children, older adults, and people who have serious health conditions are at risk for developing more serious pneumonia or life-threatening complications.

The symptoms of pneumonia may include:

• Chest pain when you breathe or cough
• Chills
• Cough with or without mucus
• Fever
• Low oxygen levels in your blood, measured with a pulse oximeter
• Shortness of breath

You may also have other symptoms, including a headache, muscle pain, extreme tiredness, nausea (feeling sick to your stomach), vomiting, and diarrhea.

Older adults and people who have serious illnesses or weakened immune systems may not have the typical symptoms. They may have a lower-than-normal temperature instead of a fever. Older adults who have pneumonia may feel weak or suddenly confused.

Sometimes babies don’t have typical symptoms either. They may vomit, have a fever, cough, or appear restless or tired and without energy. Babies may also show the following signs of breathing problems:

• Bluish tone to the skin and lips
• Grunting
• Pulling inward of the muscles between the ribs when breathing
• Rapid breathing
• Widening of the nostrils with each breath

Diagnosis

Your healthcare provider will diagnose pneumonia based on your medical history, a physical exam, and test results. Sometimes pneumonia is hard to diagnose because your symptoms may be the same as a cold or flu. You may not realize that your condition is more serious until it lasts longer than these other conditions.

Medical history and physical exam

Your provider will ask about your symptoms and when they began. They will also ask whether you have any risk factors for pneumonia. You may also be asked about:

• Exposure to sick people at home, school, or work or in a hospital
• Flu or pneumonia vaccinations
• Medicines you take
• Past and current medical conditions and whether any have gotten worse recently
• Recent travel
• Exposure to birds and other animals
• Smoking

During your physical exam, your provider will check your temperature and listen to your lungs with a stethoscope.

Diagnostic tests and procedures

If your provider thinks you have pneumonia, he or she may do one or more of the following tests:

• A chest X-ray looks for inflammation in your lungs. A chest X-ray is often used to diagnose pneumonia.
• Blood tests, such as a complete blood count (CBC) see whether your immune system is fighting an infection.
• Pulse oximetry measures how much oxygen is in your blood. Pneumonia can keep your lungs from getting enough oxygen into your blood. To measure the levels, a small sensor called a pulse oximeter is attached to your finger or ear.

If you are in the hospital, have serious symptoms, are older, or have other health problems, your provider may do other tests to diagnose pneumonia:

• A blood gas test may be done if you are very sick. For this test, your provider measures your blood oxygen levels using a blood sample from an artery, usually in your wrist. This is called an arterial blood gas test.
• A sputum test, using a sample of sputum (spit) or mucus from your cough, may be used to find out what germ is causing your pneumonia.
• A blood culture test can identify the germ causing your pneumonia and also show whether a bacterial infection has spread to your blood.
• A polymerase chain reaction (PCR) test quickly checks your blood or sputum sample to find the DNA of germs that cause pneumonia.
• A bronchoscopy looks inside your airways. If your treatment is not working well, this procedure may be needed. At the same time, your doctor may also collect samples of your lung tissue and fluid from your lungs to help find the cause of your pneumonia.
• A chest computed tomography (CT) scan can show how much of your lungs are affected by pneumonia. It can also show whether you have complications such as lung abscesses or pleural disorders. A CT scan shows more detail than a chest X-ray.
• A pleural fluid culture can be taken using a procedure called thoracentesis, which is when a doctor uses a needle to take a sample of fluid from the pleural space between your lungs and chest wall. The fluid is then tested for bacteria.

Causes

Most of the time your body filters germs out of the air that you breathe. Sometimes germs, such as bacteria, viruses, or fungi, get into your lungs and cause infections.

When these germs get into your lungs, your immune system, which is your body’s natural defense against germs, goes into action. Immune cells attack the germs and may cause inflammation of your air sacs, or alveoli. Inflammation can cause your air sacs to fill up with fluid and pus and cause pneumonia symptoms.

Bacteria

Bacteria are a common cause of pneumonia in adults. Many types of bacteria can cause pneumonia, but Streptococcus pneumoniae (also called pneumococcus bacteria) is the most common cause in the United States.

Some bacteria cause pneumonia with different symptoms or other characteristics than the usual pneumonia. This infection is called atypical pneumonia. For example, Mycoplasma pneumoniae causes a mild form of pneumonia often called “walking pneumonia.” Legionella pneumophila causes a severe type of pneumonia called Legionnaires’ diseaseexternal link. Bacterial pneumonia can develop on its own or after you have a cold or the flu.

Viruses

Viruses that infect your lungs and airways can cause pneumonia. The flu (influenza virus) and the common cold (rhinovirus) are the most common causes of viral pneumonia in adults. Respiratory syncytial virus (RSV) is the most common cause of viral pneumonia in young children.

Many other viruses can cause pneumonia, including SARS-CoV-2, the virus that causes COVID-19. Our video about how SARS-CoV-2 affects the lungsexternal link talks about this.

Fungi

Fungi such as Pneumocystis jirovecii may cause pneumonia, especially for people who have weakened immune systems. Some fungi found in the soil in the southwestern United States and in the Ohio and Mississippi River valleys can also cause pneumonia.

Risk Factors

Your risk for pneumonia may be higher because of your age, environment, lifestyle habits, and other medical conditions.

Age

Pneumonia can affect people of all ages. However, two age groups are at higher risk of developing pneumonia and having more serious pneumonia:

• Babies and children, 2 years old or younger, are at higher risk because their immune systems are still developing. This risk is higher for premature babies.
• Older adults, age 65 or older, are also at higher risk because their immune systems generally weaken as people age. Older adults are also more likely to have other chronic (long-term) health conditions that raise the risk of pneumonia.

Babies, children, and older adults who do not get the recommended vaccines to prevent pneumonia have an even higher risk.

Environment or occupation

Most people get pneumonia when they catch an infection from someone else in their community. Your chance of getting pneumonia is higher if you live or spend a lot of time in a crowded place such as military barracks, prison, homeless shelters, or nursing homes.

Your risk is also higher if you regularly breathe in air pollution or toxic fumes.

Some germs that cause pneumonia can infect birds and other animals. You are most likely to encounter these germs if you work in a chicken or turkey processing center, pet shop, or veterinary clinic.

Lifestyle habits

• Smoking cigarettes can make you less able to clear mucus from your airways.

• Using drugs or alcohol can weaken your immune system. You are also more likely to accidentally breathe in saliva or vomit into your windpipe if you are sedated or unconscious from an overdose.

Other medical conditions

You may have an increased risk of pneumonia if you have any of the following medical conditions:

• Brain disorders, such as a stroke, a head injury, dementia, or Parkinson’s disease can affect your ability to cough or swallow. This can lead to food, drink, vomit, or saliva going down your windpipe instead of your esophagus and getting into your lungs.
• Conditions that weaken your immune system may also increase your risk. These include pregnancy, HIV/AIDS, or an organ or bone marrow transplant. Chemotherapy, which is used to treat cancer, and long-term use of steroid medicines can also weaken your immune system.
• Critical diseases that require hospitalization, including receiving treatment in a hospital intensive care unit, can raise your risk of hospital-acquired pneumonia. Your risk is higher if you cannot move around much or are sedated or unconscious. Using a ventilator raises the risk of a type called ventilator-associated pneumonia.
• Lung diseases, such as asthma, bronchiectasis, cystic fibrosis, or COPD, also increase your pneumonia risk.
• Other serious conditions, such as malnutrition, diabetes, heart failure, sickle cell disease, or liver or kidney disease, are additional risk factors.

Prevention

Pneumonia can be very serious and even life-threatening. You can take a few steps to try and prevent it.

Vaccines can help prevent some types of pneumonia. Good hygiene (washing your hands often), quitting smoking, and keeping your immune system strong by getting regular physical activity and eating healthy are other ways to lower your risk of getting pneumonia.

Vaccines

Vaccines can help prevent pneumonia caused by pneumococcus bacteria or the flu virus. Vaccines cannot prevent all cases of pneumonia. However, compared to people who don’t get vaccinated, those who are vaccinated and still get pneumonia tend to have:

• Fewer serious complications
• Milder infections
• Pneumonia that doesn’t last as long

Pneumococcus vaccines

Two vaccines are available to prevent infections from the pneumococcus bacteria, the most common type of bacteria that causes pneumonia. Pneumococcus vaccines are especially important for people at high risk of pneumonia, including:

• Adults age 65 or older
• Children age 2 or younger
• People who have chronic (ongoing) diseases, serious long-term health problems, or weak immune systems. This may include people who have cancer, HIV, asthma, sickle cell disease, or damaged or removed spleens.
• People who smoke

For more information, visit the CDC’s Pneumococcal Vaccination and Pneumococcal Vaccination: Summary of Who and When to Vaccinate.

Flu (influenza) vaccine

Your yearly flu vaccine can help prevent pneumonia caused by the flu. The flu vaccine is usually given in September through October, before flu season starts.

For more information about the flu vaccine, visit the CDC’s Seasonal Influenza (Flu) Vaccination and Who Needs a Flu Vaccine and When.

Hib vaccine

Haemophilus influenzae type b (Hib) is a type of bacteria that can cause pneumonia and meningitis. The Hib vaccine is recommended for all children under 5 years old in the United States. The vaccine often is given to infants starting when they are 2 months old.

For more information about the Hib vaccine, go to the CDC’s Hib Vaccination webpage.

Other ways to prevent pneumonia