Woman with pneumonia displayed by green hue in right lung. Close-up images show normal airway and air spaces and one with pneumonia -- with narrowed airway and air spaces filled with mucus and fluid.
In a person with pneumonia, the airways (bronchi) swell and the air spaces (alveoli) fill with mucus and other fluids.

What is pneumonia?

Pneumonia is an infection in one or both of your lungs caused by bacteria, viruses or fungi. When there is an infection in the lungs, several things happen, including:

  • Your airways swell (become inflamed)
  • The air sacs in the lungs fill with mucus and other fluids

How do the lungs work?

Your lungs’ main job is to get oxygen into your blood and remove carbon dioxide. This happens during breathing. You breathe 12 to 20 times per minute when you are not sick. When you breathe in, air travels down the back of your throat and passes through your voice box and into your windpipe (trachea). Your trachea splits into two air passages (bronchial tubes). One bronchial tube leads to the left lung, the other to the right lung. For the lungs to perform their best, the airways need to be open as you breathe in and out. Swelling (inflammation) and mucus can make it harder to move air through the airways, making it harder to breathe. This leads to shortness of breath, difficulty breathing and feeling more tired than normal.

How common is pneumonia?

Approximately 1 million adults in the United States are hospitalized each year for pneumonia and 50,000 die from the disease. It is the second most common reason for being admitted to the hospital -- childbirth is number one. Pneumonia is the most common reason children are admitted to the hospital in the United States. Seniors who are hospitalized for pneumonia face a higher risk of death compared to any of the top 10 other reasons for hospitalization.

Is pneumonia contagious?

Certain types of pneumonia are contagious (spread from person to person). Pneumonia caused by bacteria or viruses can be contagious when the disease-carrying organisms are breathed into your lungs. However, not everyone who is exposed to the germs that cause pneumonia will develop it.

Pneumonia caused by fungi are not contagious. The fungi are in soil, which becomes airborne and inhaled, but it is not spread from person to person.

How is pneumonia spread from person to person?

Pneumonia is spread when droplets of fluid containing the pneumonia bacteria or virus are launched in the air when someone coughs or sneezes and then inhaled by others. You can also get pneumonia from touching an object previously touched by the person with pneumonia (transferring the germs) or touching a tissue used by the infected person and then touching your mouth or nose.

How long do I remain contagious if I have pneumonia?

If you have bacterial pneumonia, you are still considered contagious until about the second day after starting to take antibiotics and you no longer have a fever (if you had one). If you have viral pneumonia, you are still considered contagious until you feel better and have been free of fever for several days.

Who is most at risk for getting pneumonia?

People who have an increased risk of pneumonia include:

  • People over the age of 65 and infants under age 2. The weakening immune system of older people makes them less able to fight off illnesses. Similarly, the immune system of infants is still developing and not at full-strength, making them more susceptible to infection.
  • People with a health-caused weakened immune system. Examples include:
  • People who have health conditions that affect the lungs or heart. Examples include:
  • People who have neurological conditions that make swallowing difficult. These people are at risk for pneumonia caused by aspiration. Examples include:
  • People who are in the hospital. In particular, people in the ICU or anyone recovering who spends a large amounts of time lying on their backs. This position allows fluids, mucus or germs to settle in the lungs. People who need ventilators to breathe are at even greater risk since they have a difficult time coughing up germs that could cause a lung infection.
  • People who smoke or drink alcohol. Smoking damages lung tissue and long-term alcohol abuse weakens the immune system.
  • People who are exposed to toxic fumes, chemicals or secondhand smoke. These contaminants weaken lung function and make it easier to develop a lung infection.
  • Pregnant women. Being pregnant increases the risk of developing pneumonia. This is due to the immune system of a mother not working at full strength because the body is working harder to support the growth of the baby.

What causes pneumonia?

Pneumonia can be caused by a wide variety of bacteria, viruses or fungi. Pneumonia is most commonly classified by the type of germ that causes it and by the location where the person became infected.

Community-acquired pneumonia is the most common type of pneumonia. This type of pneumonia occurs outside of a hospital or other healthcare facility. Causes include:

  • Bacteria: Streptococcus pneumoniae is the most common bacterial cause of pneumonia.
  • Mycoplasma pneumoniae and other atypical bacteria: Other types of bacteria with unique features can cause different types of pneumonia. These include Mycoplasma pneumoniae (causes “walking” pneumonia), Chlamydia pneumoniae (causes Chlamydia pneumonia) and Legionella pneumoniae (causes Legionnaires’ disease).
  • Viruses: Any virus that causes a respiratory tract infection (infections of the nose, throat, trachea [windpipe], and lungs) can cause pneumonia. The viruses that cause colds and flu (influenza) can cause pneumonia.
  • Fungi (molds): Pneumonia caused by fungi is the least common as pneumonia. Fungus in the soil in certain parts of the United States can become airborne and cause pneumonia. One example is valley fever.

Hospital-acquired pneumonia develops during a stay in the hospital for another illness. This type of pneumonia can be more serious because the person is already sick and antibiotics typically used may be less effective. Bacteria adapt and change over time when exposed to antibiotics, making them less effective (called antimicrobial resistance). People in hospitals spread their drug-resistant bacteria to others, leading to more severe and difficult-to-treat cases of pneumonia. People who are on breathing machines (ventilators) are at increased risk for hospital-acquired pneumonia.

Long-term care facility-acquired pneumonia occurs in long-term care facilities (such as nursing homes) or outpatient, extended-stay clinics. Like hospitalized patients, drug-resistant bacteria are found in this setting.

Aspiration pneumonia is another type of pneumonia. Aspiration is when solid food, liquids, saliva or vomit go down the trachea (windpipe) and into the lungs instead of going down the esophagus and into the stomach. If you can’t cough up these substances, these particles remain in lung tissue and can become infected and pneumonia may develop.

What are the signs and symptoms of both bacterial and viral pneumonia?

Symptoms of pneumonia can range from mild (cold- or flu-like symptoms) sometimes called “walking pneumonia” to severe. How serious your case of pneumonia is depends on the particular germ causing the pneumonia, your overall health and your age.

Bacterial pneumonia: Symptoms of bacterial pneumonia can develop gradually or suddenly. Symptoms include:

  • High fever (up to 105° F)
  • Tiredness (fatigue)
  • Trouble breathing: rapid breathing or shortness of breath
  • Sweating
  • Chills
  • Cough with mucus (might be greenish in color or contain a small amount of blood)
  • Chest pain and/or abdominal pain, especially with coughing or deep breathing
  • Loss of appetite
  • Confused mental state or changes in awareness (especially in older adults)

Viral pneumonia: Symptoms usually develop over a period of several days. Early symptoms are similar to flu symptoms, which include:

  • Fever
  • Dry cough
  • Headache
  • Sore throat
  • Loss of appetite
  • Muscle pain
  • Weakness

Additional symptoms appearing about a day later include:

  • Higher fever
  • Cough with mucus
  • Shortness of breath

Are symptoms of pneumonia different in the very young and in seniors?

Some babies and infants with pneumonia may not show any signs of infection. When they do show symptoms, those symptoms may include:

  • Restlessness
  • Increased tiredness (fatigue)
  • Vomiting
  • Cough or fever
  • Decreased intake of fluids or food

Older adults may have milder symptoms and may not have a fever. A sudden change in mental state is sometimes a sign of pneumonia in this age group.

What are the complications of pneumonia?

Anyone can experience complications from pneumonia. However, people in high-risk groups are more likely to develop complications, including:

  • Breathing difficulties: Pneumonia can make breathing difficult. Pneumonia plus an existing lung disorder (such as COPD, emphysema, asthma) can make breathing even more difficult. Breathing difficulties may require a hospital stay to receive oxygen therapy or breathing and healing assistance with use of a breathing machine (ventilator).
  • Fluid buildup in the lungs (called pleural effusion or “water on the lungs”): Pneumonia can cause a buildup in fluid between the membranes that line the lungs and the inside of the chest cavity. It is a serious condition that makes breathing difficult. Pleural effusion can be treated by draining excess fluid with a catheter, chest tube or by surgery.
  • Bacteria in the bloodstream (bacteremia): The bacteria that cause pneumonia can leave your lungs and enter your bloodstream, spreading infection to other organs. This condition is treated with antibiotics.
  • Lung abscess. A lung abscess is a pus-filled cavity in the lung that is caused by a bacterial infection. It can be treated by draining the pus with a long needle or removing it by surgery.

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