CHICAGO (CBS) — Four people were hospitalized Thursday morning, after a fire at a nursing home in unincorporated Cook County near Des Plaines.

The fire started around 8:20 a.m. at Ballard Respiratory and Rehabilitation Center, at 9300 Ballard Rd.

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North Maine Fire Protection District officials said the fire was contained to a single unit at the nursing home, and the building’s sprinkler system extinguished the flames by the time firefighters arrived.

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Cook County Sheriff’s officials said four people were taken to the hospital. Three were seniors who suffered smoke inhalation injuries. One was an employee who suffered a sprained ankle while moving other seniors away from the fire.

Ten people living in the same wing were relocated to another part of the building, due to smoke and water damage.

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The cause of the fire was under investigation.