CHICAGO (CBS) — Three cases of Legionnaires’ disease have been diagnosed, all possibly linked to a suburban hospital.

All three were patients at Northwestern Medicine Central DuPage Hospital.

READ MORE: Gov. JB Pritzker Announces Vaccine Or Weekly Testing Mandate For Illinois Daycare Workers

The Illinois Department of Public Health is now investigating.

READ MORE: K-9, Riggs, Expected To Recover After Being Shot By Chicago Homicide Suspect During Confrontation With Kenosha County Sheriff's Deputy

Legionnaires’ spreads when people inhale water droplets contaminated with legionella bacteria.

Hospital officials are also investigating the possible causes.

MORE NEWS: No Arrests In Death Of Zion Mother Melanie Yates, Hit By A Stray Bullet