An outbreak of E. coli O157:H7 infections was linked to the consumption of hamburgers from the Jack In The Box Restaurant chain. Cases were reported from the states of Washington (602 cases/144 hospitalizations/3 deaths), Idaho (14 cases/4 hospitalizations/no deaths), California (34 cases/14 hospitalizations/1 death), and Nevada (58 cases/9 hospitalizations/no deaths). In January 1993, a physician from Children's Hospital and Medical Center, in Seattle, noted and reported to Seattle-King County Public Health personnel that there had been an increase in emergency room visits for hemolytic uremic syndrome and for bloody diarrhea. Case finding was initiated. A case control study implicated the chain's hamburgers resulting in a multistate recall of the remaining hamburgers. Only 20% of the product remained at the time of the recall; this amounted to 272,672 hamburger patties. Subsequent testing of the hamburger patties showed the presence of E. coli O157:H7. The strain of E. coli O157:H7 found in ill persons matched the strain isolated from uncooked hamburger patties. Illnesses were primarily associated with eating the regular-sized hamburger patties. A meat traceback was conducted, however no specific slaughter plant or farm was ever identified as the source of the contaminated meat. Hamburger patties had been made at one plant. The outbreak illustrated the potential for large, foodborne illness outbreaks associated with restaurant chains receiving shipments of contaminated food. There were factors that complicated the detection and subsequent response to this outbreak. At the time, many clinical laboratories in the United States were not routinely culturing stool for E. coli O157:H7 by using the correct culture medium. Additionally, many health departments were not actively tracking and investigating E. coli O157:H7 cases. E. coli O157:H7 bacteria can be killed by cooking hamburger to an internal temperature of 155 F or greater, a standard at the time. The restaurant chain was not uniformly applying this cooking standard.