CHICAGO (AP) — Health officials say an outbreak of Legionnaires’ disease at a suburban Chicago senior living center has left one elderly resident dead and two others sickened.

In a news release, the Lake County Health Department says it confirmed the three cases of the disease that is a type of severe pneumonia caused by the Legionella bacteria at the Brookdale Senior Living in Vernon Hills.

The release says the facility is contacting residents and others who may have been exposed to the bacteria as state and county health officials are trying to determine “potential sources of contamination.”