Agribusiness giant Cargill Inc. said this weekend it is recalling about 844,812 pounds of frozen beef patties due to possible E. coli contamination after investigators found four cases of illness linked to a division of Wal-Mart Stores Inc. (WMT) in Minnesota.

Wal-Mart-owned Sam's Club pulled frozen hamburgers made by Cargill from its store shelves over the weekend after Minnesota health officials discovered four cases of E. coli associated with the burgers.

Symptoms of E. coli 0157:H7 illness — the strain associated with the recall — include potentially severe stomach cramps and diarrhea.

Cargill learned of the situation on Friday and said in a statement it does not yet know the extent of "any contamination." The investigation, which has been expanded beyond Minnesota, is ongoing.

"We are concerned that some consumers may still have the product sold at retail in their freezers," Bill Rupp, president of Cargill Meat Solutions, said in a statement. "We and Sam's Club are urging customers to return or destroy any American Chef's Selection Angus Beef Patties purchased in any of their stores since August."

Cargill said the hamburgers were manufactured at its plant in Butler, Wisconsin.

All four cases of E. coli being investigated occurred in children, the Minnesota Department of Health said in a statement. The cases are associated with eating ground beef patties purchased from Sam's Club stores in late August and September.