(Oct. 14, 4:10 p.m.) The investigation of an E. coli outbreak in Michigan has shifted its focus to California.

Jennifer Holton, spokeswoman for the Michigan Department of Agriculture, said that based on shipping and delivery dates, illness onset dates and other traceback information investigators have determined that iceberg lettuce from California is believed to be the source of the outbreak.

Holton said Oct. 14 that the food and drug branch of the California Department of Public Health has started its own investigation in that state. A spokesman for the California health department could not immediately be reached for comment.

The Michigan Department of Community Health linked the outbreak to bagged, industrial-size packages of iceberg lettuce Sept. 26 and named Detroit processor Aunt Mid’s as the distributor. However, Aunt Mid’s was sourcing from multiple growers in multiple states, including California, when the outbreak started, and it was unclear at that time where the tainted product was sourced from.

Holton said Oct. 14 that it remained unclear where in the supply chain the product was contaminated.

Dominic Riggio, Aunt Mid’s president, said the company resumed processing iceberg lettuce Oct. 9.

Holton said Oct. 14 that Aunt Mid’s will test each lot of the product for 30 days and report the findings to the state department of agriculture, which also will perform random tests during that period.

There have been 38 reported illnesses in Michigan and 21 hospitalizations. There also have been nine illnesses reported in Illinois and three in Ontario. No deaths have been associated with the outbreak.