In late July and early August 2006, the Minnesota Department of Health (MDH) received three E. coli O157:H7 stool isolates from residents of, and visitors to, Longville, Minnesota. Pulsed-field gel electrophoreses (PFGE) patterns for all three were indistinguishable, and the pattern had never been seen before in Minnesota. At the same time, MDH learned of an outbreak of gastrointestinal illnesses among members of the Salem Lutheran Church in Longville. The church had served meals on July 10 and 19, and multiple congregation members subsequently fell ill with cramps and bloody diarrhea.
The MDH opened an epidemiologic and environmental health investigation of the three confirmed E. coli O157:H7 illnesses and the church outbreak. MDH obtained the member directory from the church and interviewed parishioners to obtain information concerning their attendance at church events along with a general food and activity history. In addition, an MDH sanitarian visited the Salem Lutheran Church to conduct an environmental assessment of the kitchen where the food for the July 19 meal had been prepared. The Minnesota Department of Agriculture (MDA) contacted local grocery stores and restaurants to obtain information on the type and source of beef products involved.
MDA and MDH learned that ground beef used to make meatballs for the church meal, as well as the ground beef purchased by numerous area restaurants, was purchased at Tabaka’s Supervalu. On July 17, members of the church had purchased 40 pounds of ground beef from the Supervalu. MDA conducted an on-site inspection at the store on August 7, 2006.
MDH’s epidemiological investigation revealed seventeen illnesses that met the case definition. Of these, three people developed hemolytic uremic syndrome (HUS), and one patient died. Attendance at the church’s July 19 smorgasbord dinner was significantly associated with illness.
MDA conducted a traceback of the ground beef purchased at the Supervalu and used in the July 19 meal. The store had received approximately 1,900 pounds of chuck rolls from distributor Interstate Meat on July 10. The majority of the chuck rolls were ground into ground beef at the Supervalu. The Supervalu sold ground beef from the July 10 shipment to three Longville restaurants in the same time period as the sale to church members. Supervalu did not receive any chuck rolls from any distributor other than Interstate Meat in the weeks prior to the outbreak.
The MDA traceback of the chuck rolls from Interstate Meat revealed that the “most plausible” source of the chuck rolls delivered to the Supervalu was the Nebraska Beef processing plant. In addition to this, the USDA reported that a sample of beef trimmings collected on June 14, 2006 at a processing plant cultured positive for E. coli O157:H7, and that the isolate was indistinguishable by PFGE analysis to the outbreak strain. The processing plant was determined to be Nebraska Beef, the company that most likely supplied the implicated chuck rolls to Tabaka’s Supervalu.
Ultimately, MDH concluded that:
•“There was an outbreak of E. coli O157:H7 infections among members of the Longville, Minnesota community.
•Ground beef from Tabaka’s Supervalu was the “source of E. coli O157:H7 for this outbreak.”
•“The isolation of the rare outbreak PFGE subtype of E. coli O157:H7 from a sample of beef trimmings from a USDA-inspected plant in the weeks prior to the outbreak suggests that the chuck rolls that were used to produce the ground beef at the store were likely already contaminated when received by the store.”
•“…records that were available from the Tabaka’s Supervalu and [Interstate Meat] suggested that the ultimate source of the implicated chuck rolls was [Nebraska Beef].