The Michigan Department of Community Health said Thursday it is investigating eight unconfirmed cases of the E. coli 0157:H7 bacterial infection. Four more cases in Ohio are pending confirmation from health officials there.
The Kroger Co. announced Wednesday it was recalling all ground beef products with sell-by dates between May 21 and June 8.
So far, at least 35 people have been infected with the same strain of E. coli found in contaminated Kroger meat, according to Michigan and Ohio health departments.
Kroger declined Thursday to release the number of meat suppliers it works with to supply its more than 2,470 supermarkets and stores in 31 states.
The U.S. Department of Agriculture's Food Safety and Inspection Service would not release information about the number or names of suppliers undergoing investigation, citing Kroger's proprietary business relations.
"What is important for consumers is the recall release," Amanda Eamich, spokeswoman for the inspection agency.
She added that investigators are working around the clock to identify the source.
Kroger has been involved in at least four ground beef recalls involving meat suppliers and processors in the past, according to the Cincinnati-based grocer's news release archives.
In July 2002, Kroger recalled all of its ground beef products because one of its suppliers, ConAgra Beef, one of the nation's largest beef processors, found E. coli in a sample of its meat.
In August 2001 and December 2000, Kroger recalled ground beef because meat from American Foods Group Inc., a wholesale meat supplier based in Green Bay, Wis., was found to have the same strain of bacteria.
Within days of the American Foods recall in August 2001, Kroger also recalled ground beef after IBP Inc., a wholesale meat supplier based in Dakota City, Neb., found E. coli in some of its meat products.