CDC collaborated with public health officials in California, Michigan, Minnesota, Wisconsin, and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of E. coli O157:H7 infections. Investigators used DNA analysis of E. coli O157:H7 bacteria obtained through diagnostic testing to identify cases of illness that may have been part of this outbreak.

As of April 1, 2011, eight persons infected with the outbreak strain of E. coli serotype O157:H7 were reported from Michigan (1), Minnesota (3), and Wisconsin (4). Reported dates of illness onset range from December 20, 2010 to February 16, 2011. Ill persons ranged in age from 15 to 78 years, with a median age of 63 years; 75% were male. Among ill persons, 50% reported being hospitalized, and none reported hemolytic uremic syndrome, which is a type of kidney failure that is associated with E. coli O157:H7 infections. No deaths were reported.

Collaborative investigative efforts of local, state, and federal public health and regulatory agencies associated this outbreak with eating in-shell hazelnuts (also known as filberts). Most of the in-shell hazelnuts were purchased from bulk bins at retail food stores. Source tracing identified a common distributor for the hazelnuts consumed by ill persons: DeFranco & Sons in Los Angeles, California. Laboratory testing conducted by the Minnesota Department of Agriculture on in-shell hazelnuts, the California Department of Public Health on mixed nuts containing in-shell hazelnuts, and the Wisconsin Department of Health Services on mixed nuts containing in-shell hazelnuts identified E. coli O157:H7 matching the outbreak strain by DNA analysis.