It affects millions of people every year, but is pneumonia contagious? Or does it occur for some other reason in so many people?
The answer is not very straightforward. Generally, a healthy person will not get pneumonia just by being exposed to someone else with pneumonia. But they could still get sick.
To understand if pneumonia is contagious, you have to understand what pneumonia is and how it affects a person.
Pneumonia means there is an inflammation of the lungs. There are actually over 30 different types of pneumonia. It is not one single disease caused by one germ. Pneumonia can be bacterial, viral, fungal, caused by a mycoplasm or even chemicals. The cause of the pneumonia relates to whether or not it is contagious.
Bacterial pneumonia sometimes occurs when a person has some other type of infection (either bacterial or viral) that weakens their immune system. It can also occur on its own without a preceding infection.
In many cases, the bacteria that causes the pneumonia may not cause pneumonia in another healthy person, but it (or the other viral/bacterial infection) could be contagious and cause less serious symptoms, such as an upper respiratory infection.
Viral pneumonia is similar to bacterial pneumonia regarding how contagious it is. If a healthy person is exposed to someone with viral pneumonia, they may get sick, but it will not necessarily turn into pneumonia.
Mycoplasma pneumonia is caused by an organism that is somewhere between a bacteria and a virus. The symptoms of mycoplasma pneumonia are typically mild, but it is contagious. If you have mycoplasma pneumonia, you should not expose yourself to infants, older adults or people with weakened immune systems.
Pneumonia caused by chemicals or inhalants is not contagious. It can be quite serious for the person who is affected but cannot be passed to another person through casual contact.
In general, being exposed to someone with pneumonia does not mean you will get pneumonia, but you could get sick with a less serious illness. Infants, older adults and those with weakened immune systems are more likely to contract pneumonia and suffer serious symptoms from it.
To protect yourself and others, be sure to wash your hands frequently, especially after blowing your nose, going to the bathroom, diapering a baby, and before eating or preparing foods.
"Pneumonia." Kids Health 2011. Nemours Foundation. 25 Apr 11.
"Understanding Pneumonia." Lung Disease 2011. American Lung Association. 25 Apr 11.