On September 12, 2005 Public Health Seattle King County received an unusual number of E. coli O157:H7 reports. Case interviews by county investigators subsequently revealed that three unrelated residents of King County and one Pierce County resident had all eaten at the same Olive Garden restaurant in Federal Way on September 1, 2005. All four cases became ill on September 5, and two were hospitalized. Detailed food histories were obtained. The common foods consumed by the four ill individuals were the house salad and fresh parsley used either as a topping or as an ingredient in entrees. Pulsed field gel electrophoresis (PFGE) analysis of isolates obtained from patients’ stool cultures was conducted at the Washington Department of Health (WDOH) Public Health Laboratory (PHL). Results showed that all four patients were infected with the same strain of E. coli O157:H7 and shared indistinguishable PFGE patterns derived from restriction by two enzymes. The WDOH PHL assigned state identification number EC472 to the outbreak patterns.

The investigation might have ended with only a cursory report to the Centers for Disease Control and Prevention (CDC), but on September 29, 2005 the WDOH was notified that two more persons were hospitalized with bloody diarrhea and presumed to have E. coli O157:H7. The two individuals were unrelated and lived in Kitsap County. Both had eaten at The Boat Shed restaurant on September 10. Laboratory testing would soon confirm infection with E. coli O157:H7 and PFGE analysis linked the infection to the four Olive Garden cases reported in mid-September. Environmental inspections and food histories obtained by Kitsap County environmental health specialists identified common foods consumed by the cases. These included salad ingredients and a common garnish, parsley, served with each person’s entree.
PFGE subtyping would reveal that two additional Washington residents with laboratory confirmed E. coli O157:H7 were part of the cluster. One person lived in Clark County and experienced onset of illness on August 23, 2005; the other person lived in Whatcom County and became ill on September 7, 2005. Seven of the eight individuals identified in the outbreak had eaten fresh parsley served in three separate restaurants. Both the Xba1 and Bln1 PFGE patterns had not been seen previously in Washington and had not yet been seen in other states.
WDOH environmental health staff conducted a trace back of suppliers of produce at the three restaurants where exposure to E. coli O157:H7 had occurred. Parsley was the only item that had been supplied by a single grower. On October 12 the FDA district office located in Bothell, Washington was briefed on WDOH findings. The FDA contacted the Food Safety Division at the Oregon Department of Agriculture (ODA). ODA staff pursued information regarding product distribution, dates of growing cycles, and production issues potentially related to product contamination.
Health officials in Oregon, aware of the outbreak in Washington State, noticed an increase in E. coli O157:H7 cases in mid-October. More than 20 persons who lived in the Bend, Oregon area were reporting diarrhea. The Deschutes Health Department investigated and found that all of the ill individuals had eaten at McGrath’s Fish House between October 12 and October 14, 2005. Two of the individuals had submitted stool specimens which cultured positive for E. coli O157:H7. A case-control study was conducted among persons reporting illness and people who were not ill. Data analysis implicated parsley served in food or as a garnish as the source of E. coli O157:H7 among McGrath’s Restaurants patrons. The association with parsley was strengthened further by PFGE analysis which showed that individuals who became ill with E. coli O157:H7 after eating at McGrath’s Restaurant were infected with the same strain of E. coli O157:H7 that infected Washington state residents in September. Furthermore, Oregon health investigators traced the source of the parsley served at McGrath’s to the same farm that supplied parsley to the Olive Garden and The Boat Shed, restaurants associated with E. coli O157:H7 illness in Washington residents.