title: Use of traceback methods to confirm the source of a multistate Escherichia coli O157:H7 outbreak due to in-shell hazelnuts.
abstract: Traceback methods by state regulatory agencies were used to complement traditional epidemiological cluster investigation methods and confirmed hazelnuts (also referred to as filberts) as the vehicle in a multistate outbreak of Escherichia coli O157:H7 infections. Bulk in-shell  hazelnut and mixed-nut purchase locations were identified during the initial epidemiological interviews. Based on purchase dates and case onset dates, regulators in Minnesota, Michigan, and Wisconsin traced product back through the supply chain. Six (86%) retail locations received the suspect  hazelnut or mixed-nut shipments from a Minnesota distributor, with one retailer (14%) receiving products from a Wisconsin distributor. Both distributors received 100% of their bulk in-shell hazelnuts and mixed nuts from a distributor in California. The California distributor received 99% of  their hazelnuts from a packing company in Oregon. The California distributor received the hazelnuts in 50-lb (22.7-kg) bags and either resold them without opening the bags or used the in-shell hazelnuts in the manufacture of their in-shell mixed nuts. Records at the packing company in Oregon  were incomplete or lacked sufficient detail needed to identify a suspect farm or group of suspect farms. Laboratory samples collected from human cases and subsequently recalled product matched the outbreak pulsed-field gel electrophoresis subtype of E. coli O157:H7. Hazelnut harvesting  practices create a plausible route of contamination from fecal matter from domestic ruminants or wild deer. This outbreak investigation demonstrates the use of product traceback data to rapidly test an epidemiological hypothesis.
authors.affiliation: Minnesota Department of Agriculture, Saint Paul, MN 55155, USA. Benjamin.miller@state.mn.us
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Miller
authors.forename: Carrie E
authors.initials: CE
authors.lastname: Rigdon
authors.forename: Jill
authors.initials: J
authors.lastname: Ball
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Rounds
authors.forename: Rachel F
authors.initials: RF
authors.lastname: Klos
authors.forename: Brenda M
authors.initials: BM
authors.lastname: Brennan
authors.forename: Katherine D
authors.initials: KD
authors.lastname: Arends
authors.forename: Patrick
authors.initials: P
authors.lastname: Kennelly
authors.forename: Craig
authors.initials: C
authors.lastname: Hedberg
authors.forename: Kirk E
authors.initials: KE
authors.lastname: Smith
mesh_terms: D002140:California; D031211:Corylus / Q000382:microbiology*; D004196:Disease Outbreaks; D004927:Escherichia coli Infections / Q000453:epidemiology* / Q000382:microbiology; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D005517:Foodborne Diseases / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D009922:Oregon