CINCINNATI --- The Kroger Co. expanded its voluntary recall of some ground beef products beyond stores in Michigan and parts of Ohio to its stores in more than 20 states on Wednesday.

The nation's biggest traditional grocer also urged customers to check the ground beef in their refrigerators and freezers for the date by which the product must be sold.

Meat obtained from one of Kroger's suppliers, Nebraska Beef Ltd., has been linked to illness reported in Michigan and Ohio between May 31 and June 8 caused by the E. coli bacteria.

Nebraska Beef has recalled from wholesalers and other processing companies nearly 532,000 pounds of ground beef produced on five dates between May 16 and June 24.

Kroger said Wednesday that as a precaution it had removed ground beef supplied by Nebraska Beef from its stores.

"Ground beef in stores today comes from other suppliers not involved in the recall," Kroger spokeswoman Meghan Glynn said Wednesday.

The Cincinnati-based company advised customers to look for "sell buy" dates from mid-May through early July on most ground beef products they have purchased from its stores and return them.

Kroger initiated the recall June 25 for stores in Michigan and in central and northern Ohio. The expanded recall includes ground beef sold at Fred Meyer, QFC, Ralphs, Smith's, Baker's, King Soopers, City Markets, Hilander, Owen's, Pay Less and Scott's.

In some stores, the recall includes products in foam tray packages wrapped in clear cellophane or purchased from an in-store service counter. It does not include ground beef sold in sealed tubes in 1, 3 or 5-pound packages and frozen ground beef patties sold in the frozen food section of its stores.

Kroger is notifying customers about the expanded recall by placing signs in meat departments. It also is using its register receipt notification system.

Symptoms of E. coli infection can include severe stomach cramps, diarrhea, vomiting and fever. Most people recover within 5 to 7 days.

Health officials urge people to thoroughly cook hamburger to at least 160 degrees.