(CBS) – A number of deaths and frostbite cases are being attributed to the snowstorms that walloped the Chicago region late last week and the lingering subzero cold snap that followed.

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In southwest suburban Will County, three men ranging in age from 57 to 63 died after shoveling snow in Bolingbrook and Joliet, the coroner’s office tells CBS 2. All three were taken to hospitals before they died from apparent exertion.

A 48-year-old Chicago man died under similar circumstances after shoveling snow late Sunday in the Humboldt Park neighborhood, Chicago police said. He had a history of heart problems.

Meanwhile, hospitals in Chicago and the suburbs confirm cases of frostbite, ranging from serious to mild.

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At Cook County’s Stroger Hospital, doctors admitted a 60-year-old homeless man suffering frostbite on his feet and one hand.

Homeless people are particularly vulnerable, says Stroger emergency-room physician Michelle Sergel. With the types of subzero air temperatures felt Monday, frostbite can set in within minutes.

Symptoms to watch out for include discoloration of extremities and decrease of sensations or intense pain, Sergel says.

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Also, hospitals say they have seen patients for cold-related injuries that have included back pain attributed to snow-shoveling.