Pneumonia Causes and Risks

What Causes Pneumonia?

Pneumonia has many possible causes. The most common are bacteria and viruses in the air we breathe. Your body usually prevents these germs from infecting your lungs. But sometimes these germs can overpower your immune system, even if your health is generally good.

There are 4 different types of pneumonia. Pneumonia is classified according to the types of germs that cause it, and where you acquired the infection.

  • Community-Acquired Pneumonia
    This type the most common type of pneumonia. You can catch it in public areas (such as work, school, the grocery store or the gym). Bacteria, a virus, fungi or irritants in the air can cause community-acquired pneumonia. This type of pneumonia can also develop after you have a cold or the flu.
  • Hospital-Acquired Pneumonia or Institution-Acquired Pneumonia
    It is the type of pneumonia you can catch while staying in the hospital, especially if you are in the ICU or are using a ventilator to assist your breathing. This type of pneumonia also includes pneumonia that develops after you have major surgery. It can be very dangerous, especially for young children, older adults and people who have weakened immune systems.
  • Aspiration Pneumonia
    This type of pneumonia develops after you inhale particles into your lungs. This occurs most often when small particles enter your lungs after vomiting and you are not strong enough to cough the particles out of your lungs.
  • Opportunistic Pneumonia
    It is a type of pneumonia that affects people who have weakened immune systems. It is caused by certain organisms that do not typically make healthy people sick, but they can be dangerous for people who have conditions such as the human immunodeficiency virus (HIV), acquired immunodeficiency syndrome (AIDS), chronic obstructive pulmonary disease (COPD) or people who have recently had an organ transplant.

Risk Factors

Pneumonia can affect anyone. The two age groups that are at the highest risk are infants and children younger than the age of 2 because their immune system is still devolving. Also people who are older than 65 years old are more at risk because as you get older your immune system becomes less able to fight off infections.

Other risk factors are certain chronic diseases, such as asthma, chronic obstructive pulmonary disease and heart disease. A weakened or suppressed immune system, due to factors such as HIV/AIDS, a organ transplant, chemotherapy for cancer, or long term steroid use. Smoking damages your body’s natural defenses against the bacteria and viruses that cause pneumonia.

Last Updated: February 23, 2017