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Pneumonia is an inflammation of the air sacs in the lungs (alveoli) and the surrounding tissue. It often leads to a sudden high fever, the feeling that you are very unwell, a cough and shortness of breath.

Because pneumonia is usually caused by bacteria, it can generally be treated effectively with antibiotics. Vaccinations that can prevent infection by certain germs are also available.

People who are otherwise in good health generally recover within a few weeks. But pneumonia shouldn't be taken too lightly: it can last one or sometimes even several months until you are back to full strength.

Pneumonia may sometimes have life-threatening complications, especially if you have already been weakened by another illness. Pneumonia can also be dangerous for babies and older people.

Image: Pneumonia in the left lung

Pneumonia in the left lung


Chest pain when you breathe or cough.

Confusion or changes in mental awareness (in adults age 65 and older)

Cough, which may produce phlegm.


Fever, sweating and shaking chills.

Lower than normal body temperature (in adults older than age 65 and people with weak immune systems)

Nausea, vomiting or diarrhea.


Pneumonia is usually caused by bacteria – and most frequently by bacteria called pneumococci. Sometimes, other types of bacteria such as Haemophilus influenzae or Mycoplasma pneumoniae are also involved. If you develop pneumonia in the hospital, it's often caused by an infection of bacteria that are harder to treat.

If the airways are already infected by other germs, for example flu viruses, it's easier for the bacteria to grow there. This can result in bacterial pneumonia. It's less common for pneumonia to be caused by viruses alone. Pneumonia caused by fungi is even rarer. That mainly occurs if the immune system is especially weak, for example due to AIDS.

The germs enter the lungs when tiny droplets of saliva or water are inhaled (droplet infection). But people can also become ill because they swallowed the wrong way. Then germs from the mouth and throat, and food residue or material from the stomach can enter the airways and lead to pneumonia. The medical term for this is aspiration pneumonia.

Only rarely does a bacterial infection spread through the bloodstream from elsewhere in the body to the lungs. Pneumonia caused by things besides germs, such as radiation, inhaled poisonous substances, allergic reactions or circulation problems in the lungs, is also rare.

Risk factors

The risk of developing pneumonia is particularly high in babies and older people (over 65 years). A weakened immune system, for example due to diabetes, kidney problems or cancer, also means that the risk is higher greater. Lung diseases such as asthma and COPD, heart diseases, smoking and certain viral infections such as the flu (influenza) can make people more prone to pneumonia.

The risk of aspiration pneumonia is especially high in people who are bedridden  or affected by confusion or difficulties swallowing due to dementia or stroke, for instance.

Some medications are also linked to pneumonia, such as medicines that reduce the level of acid in the stomach. But it's still not clear whether they actually increase the risk of pneumonia.

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Pneumonia may cause complications, especially in people with weakened immune systems or chronic conditions, such as diabetes.

Complications may include:

Worsened chronic conditions. If you have certain preexisting health conditions, pneumonia could make them worse. These conditions include congestive heart failure and emphysema. For certain people, pneumonia increases their risk of having a heart attack.

Bacteremia. Bacteria from the pneumonia infection may spread to your bloodstream. This can lead to dangerously low blood pressure, septic shock, and, in some cases, organ failure.

Lung abscesses. These are cavities in the lungs that contain pus. Antibiotics can treat them. Sometimes they may require drainage or surgery to remove the pus.

Impaired breathing. You may have trouble getting enough oxygen when you breathe. You may need to use a ventilator.

Acute respiratory distress syndrome. This is a severe form of respiratory failure. It’s a medical emergency.

Pleural effusion. If your pneumonia isn’t treated, you may develop fluid around your lungs in your pleura, called pleural effusion. The pleura are thin membranes that line the outside of your lungs and the inside of your rib cage. The fluid may become infected and need to be drained.

Kidney, heart, and liver damage. These organs may be damaged if they don’t receive enough oxygen, or if there’s an overreaction of the immune system to the infection.


In many cases, pneumonia can be prevented.


The first line of defense against pneumonia is to get vaccinated. There are several vaccines that can help prevent pneumonia.

Prevnar 13 and Pneumovax 23

These two pneumonia vaccines help protect against pneumonia and meningitis caused by pneumococcal bacteria. Your doctor can tell you which one might be better for you.

Prevnar 13 is effective against 13 types of pneumococcal bacteria. The CDCTrusted Source recommends this vaccine for:

children under age 2

people between ages 2 and 64 with chronic conditions that increase their risk of pneumonia

adults ages 65 and older, on the recommendation of their doctor

Pneumovax 23 is effective against 23 types of pneumococcal bacteria. The CDCTrusted Source recommends it for:

adults ages 65 and older

adults ages 19 to 64 who smoke

people between ages 2 and 64 with chronic conditions that increase their risk of pneumonia

Flu vaccine

Pneumonia can often be a complication of the flu, so be sure to also get an annual flu shot. The CDCTrusted Source recommends that everyone ages 6 months and older get vaccinated, particularly those who may be at risk of flu complications.

Hib vaccine

This vaccine protects against Haemophilus influenzae type b (Hib), a type of bacterium that can cause pneumonia and meningitis. The CDCTrusted Source recommends this vaccine for:

all children under 5 years old

unvaccinated older children or adults who have certain health conditions

people who’ve gotten a bone marrow transplant

According to the National Heart, Lung, and Blood InstituteTrusted Source, pneumonia vaccines won’t prevent all cases of the condition.

But if you’re vaccinated, you’re likely to have a milder and shorter illness as well as a lower risk of complications.

Other prevention tips

In addition to vaccination, there are other things you can do to avoid pneumonia:

If you smoke, try to quit. Smoking makes you more susceptible to respiratory infections, especially pneumonia.

Regularly wash your hands with soap and water for at least 20 seconds.

Cover your coughs and sneezes. Promptly dispose used tissues.

Maintain a healthy lifestyle to strengthen your immune system. Get enough rest, eat a balanced diet, and get regular exercise.