Pneumonia is an infection of the lung tissue that can make it difficult to breathe due to inflammation, fluid, and pus. Viruses or bacteria, which are contagious, cause most forms of pneumonia.

Not all cases of pneumonia are contagious, however, and the period during which it can spread from one person to another depends on the cause of the infection.

Contents of this article:

Is pneumonia contagious?

Pneumonia refers to an infection in the lungs caused by certain germs, such as bacteria or viruses. When one person spreads germs that can cause pneumonia to someone else, the recipient can develop a range of respiratory infections, from mild cold symptoms to pneumonia.

A range of factors determine whether pneumonia is contagious:

Type of pneumonia

senior man in bed with the flu
Contagious viruses or bacteria cause most forms of pneumonia.

Most cases of pneumonia are due to the spread of bacteria and viruses. Bacteria are living organisms that respond to antibiotics. Viruses are tiny strands of protein and genetic material that cannot be treated with antibiotics. Both viruses and bacteria are contagious.

Pneumonia often develops after a person has had a different infection, such as a head cold. This makes a person more vulnerable to other types of infections. An infection that develops in the lungs is called pneumonia.

Some organisms are more likely to cause pneumonia than others. One common example is pneumococcal disease, a bacterial infection that can cause ear infections, sinus infections, infections of the brain and blood, and pneumonia.

Another type of bacteria called Mycoplasma pneumoniae can cause other forms of pneumonia. Mycoplasma bacteria are also contagious.

The influenza virus or the flu is a common cause of viral pneumonia. The virus spreads easily from person to person, causing a range of symptoms and conditions.

Less common causes of pneumonia include:

  • inhaling food particles or contents from the intestinal tract
  • some fungi

These forms of pneumonia are not contagious.

Length of infection

In most cases, infections are contagious for a few days before symptoms appear and for a few days after. The exact length of time a person is contagious depends on the type of microorganism causing the infection.

Some forms of pneumonia, such as pneumonia caused by mycoplasma, remain contagious for several weeks. If a person has pneumonia, they should speak to a doctor about how long the infection will be contagious.

Pneumonia treatment

People with bacterial pneumonia will usually be prescribed antibiotics that stop the infection from progressing. Pneumonia will usually stop being contagious a day or two after treatment begins.

A person is also considered contagious during a fever, so it is best to stay home from work or school until the fever is gone.

People who have been vaccinated against infections that can cause pneumonia, such as pneumococcal bacteria, are usually immune to those specific germs. Getting the vaccination can help prevent this type of infection from developing.

Risk factors