Cold Home > Is Pneumonia Contagious?

People with pneumonia can transmit their germs to others. However, in most cases, the germs don't cause pneumonia; rather, they cause a milder infection, such as the common cold. In theory, the contagious period for pneumonia lasts about two weeks, although a person tends to be most contagious when symptoms are at their worst -- which is usually around day two to four of the infection.

How Contagious Is Pneumonia?

A person with either viral or bacterial pneumonia is contagious. However, that person's germs are more likely to cause an upper respiratory infection (such as the common cold or the flu) in another person than pneumonia.
Let's explain. Many of the viruses and bacteria that cause pneumonia are the same ones that cause upper respiratory infections. These germs are usually found in the mouth and nose of the infected person. They can be spread easily to another person, either through the air or by touching a contaminated surface. Most often, they enter the person's body through the mouth, nose, or eyes.
When this happens, a battle begins. The person's immune system tries to kill the germs, while the germs try to multiply. The germs also try to spread to other parts of the body, such as the lungs and blood. In most cases, however, the body prevents this, so if a person does develop symptoms, they are usually limited to where the infection entered the body (see Cold and Flu Symptoms).

Why Do Some People Get Pneumonia and Others Don't?

While the body has an advanced system for getting rid of potentially harmful substances that make their way into the lungs, it is not perfect. In some cases, so many bacteria or viruses get into the lungs that the defense systems are simply overwhelmed.
In other cases, certain diseases can make the system unable to function as well as normal. This can be from chronic diseases like diabetes or chronic obstructive pulmonary disease (COPD) or diseases that affect the immune system, such as HIV or AIDS. Other times, the particular bacteria or virus is just so potent that the body can't handle it.
With any of these situations, a person has a greater risk of developing pneumonia.
(Click Pneumonia Risk Factors to learn about other things that increase a person's risk for this condition.)
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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