In May 2007, Minnesota Department of Health (MDH) investigators detected a cluster of clinical isolates of E. coli O157:H7 with indistinguishable pulsed-field gel electrophoresis subtype pattern combination EXHX01.0047/EXHA26.0015.

Seven cases and 21 matched controls were enrolled in a case-control study. All seven patients reported consumption of ground beef during the week prior to illness onset compared with 15 of 21 controls. This association was not statistically significant. However, consumption of ground beef purchased at Grocery Chain A or Grocery Chain B was statistically significant ((6 of 7 case-patients vs. 4 of 21 controls; OR, 25.5; 95% CI, 2.4 to 619; p = 0.003). Grocery Chain A and Grocery Chain B are high-end grocery stores in the Minneapolis/St. Paul metropolitan area, are owned by the same company, and share common distributors.

Ultimately 10 outbreak associated cases were identified. Illness onset dates ranged from March 27, 2007 through May 4, 2007. Seven patients were hospitalized. No one died. No cases of hemolytic uremic syndrome (HUS) occurred.

Five samples of ground beef were collected from three culture-confirmed case-patients and
submitted to the Minnesota Department of Agriculture (MDA) Laboratory for culture during the
outbreak investigation. The MDA Laboratory isolated E. coli O157:H7 with the outbreak PFGE
pattern from one opened ground beef package with a sell-by-date of April 19, 2007, and one
intact ground beef package with a sell-by-date of April 22, 2007. Both packages were purchased
at the same Grocery Chain B in Minnetonka, Minnesota; they were submitted by two different
case-patients.

A traceback investigation by MDA and the United States Department of Agriculture Food Safety
and Inspection Service (USDA-FSIS) found that all the beef trim used for ground beef in the
implicated Grocery Chain A and Grocery Chain B stores originated from a single slaughter
facility located in Windom, Minnesota. On May 10, the slaughter facility issued a voluntary
recall of 117,500 pounds of beef trim that was produced on March 27 and distributed to
distributors and retail outlets in eight states (Arizona, Illinois, Iowa, Michigan, Minnesota, Ohio,
Virginia, and Wisconsin). Subsequently, the USDA isolated E. coli O157:H7 with the outbreak
PFGE pattern from a product sample within the plant. The plant was issued a Notice of Intended
Enforcement (NOIE). The NOIE listed a number of food safety issues that the plant needed to
address within a set time period or face the possibility of USDA-FSIS removing inspectors from the plant.