Legionnaires’ disease, a type of severe pneumonia, is caused by breathing in small droplets of water that contain Legionella. 

Most healthy people do not get Legionnaires’ disease after being exposed to Legionella. Being 50 years or older or having certain risk factors can increase your chances of getting sick. These risk factors include: ► Being a current or former smoker
► Having chronic lung disease, such as emphysema or chronic obstructive pulmonary disease (COPD) 
► Having a weakened immune system from diseases like cancer, diabetes, or kidney failure
► Taking medication that weakens your immune system

Outbreaks of Legionnaires’ disease are often associated with large or complex water systems, like those found in hospitals, hotels, and  cruise ships.