On Apr. 16, 1993, the U.S. Centers for Disease Control (CDC) reported that from November 15, 1992, through February 28, 1993, more than 500 laboratory-confirmed infections with E. coli O157:H7 and four associated deaths occurred in four states — Washington, Idaho, California, and Nevada. On January 18, 1993, a multistate recall of unused hamburger patties from the Jack in The Box restaurants in Seattle was initiated.

A meat traceback by a CDC team identified five slaughter plants in the United States and one in Canada as the likely sources of carcasses used in the contaminated lots of meat and identified potential control points for reducing the likelihood of contamination.

The outbreak strain of E. coli O157:H7 was isolated from 11 lots of patties produced on those two dates; these lots had been distributed to restaurants in all states where illness occurred. Approximately 272,672 (20%) of the implicated patties were recovered by the recall. The animals slaughtered in domestic slaughter plants were traced to farms and auctions in six western states. No one slaughter plant or farm was identified as the source.