1. Environmental Health Investigations: Conducting Traceback Investigations

2. Goals Describe the basic steps of conducting a traceback investigation Identify when it is appropriate to conduct a traceback investigation Provide examples of recent outbreak investigations that carried out traceback investigations

3. Quick review: Traceback Investigations Process used to determine the production and distribution chain of a vehicle implicated in an outbreak. Helps determine if (and where) you can conduct an environmental health assessment Used to clarify the point at which the implicated vehicle may have become contaminated

4. Traceback Investigations Identify: Places where the implicated vehicle has been AND If the vehicles to which different cases have been exposed had places in common Identification of a common place strongly suggests contamination at/before that point in production or distribution of the vehicle

5. Traceback Investigations Do not identify the source of the problem/contamination Tell investigators where to look Further investigation/inspection is necessary to identify contributing factors or implement control measures

6. Traceback Investigation Example 1 1994: Nationwide outbreak of Salmonella Enteritidis associated with a particular brand of ice cream. (1) Ice cream obtained by cases in 41 states from multiple warehouses across the country BUT, all ice cream eaten by cases prepared in one plant in Minnesota

7. Traceback Investigation Example 1 (cont.) Implicated plant obtained ice cream pre-mix shipped via truck from two suppliers Identification of a common ice cream plant suggested contamination with S. Enteritidis occurred at or before that point in the production such as: Plant Tanker trucks Pre-mix suppliers Follow-up assessments found problems with inadequate cleaning of tanker trucks that were also used to carry non-pasteurized eggs

8. Traceback Process Begins with information from cases about the implicated vehicle Extends backwards in time All points in the production and use of the vehicle are considered: Retailers Point of service establishments (e.g. restaurants) Distributors Importers Producers

9. Vehicle Distribution Patterns Distribution patterns may be complex: Retailers may obtain vehicle from more than one distributor, distributors may change over time Distributors may have multiple sources, may supply to other distributors Producers may be domestic or foreign

10. Traceback Investigation Example 2 1997: E. coli 0157:H7 outbreak in Michigan (2) Case-control study revealed strong association with eating alfafa sprouts Traceback investigation initiated by collecting data from cases: Places sprouts were purchased/eaten Locations of said establishments Dates of purchase/consumption

11. Traceback Investigation Example 2 (cont.) Investigators used store and restaurant records to identify likely sprouting facilities for implicated sprouts Source of sprouts traced for all 16 patients: Source = Facility A for 15 patients Source = Facility B for 1 patient Seed sources identified: Facility A: 2 seed lots (Idaho & Australia) Facility B: multiple seed lots

12. Traceback Investigation Example 2 (cont.) Concurrent outbreak of E.coli O157:H7 in Virginia, also tied to alfafa sprouts Source of sprouts for 13 VA patients traced to a single sprouting facility in VA using seed lot from Idaho, same as in Facility A in Michigan Facility B determined to have used Idaho seeds also, but only for 2 days Conclusion: problem resided in seeds from Idaho

13. Identification of Products Clear identification of implicated products is essential to a traceback Branded (commercial) products do not always provide clear identification If package is not available, consumers may not remember exact name One product may be repackaged and distributed under different names

14. Traceback Investigation Example 3 1998: 49 cases of Salmonella Agona reported in Illinois (3) Nine other states also had increases in S. Agona PFGE subtyping suggested cases had common origin Matched case-control study linked S. Agona infections with consumption of cereal but no common brands were noted

15. Traceback Investigation Example 3 (cont.) Traceback investigation revealed implicated cereal was produced by a Minnesota company, Malt-O-Meal Cereal sold under brand name Toasty-O’s ® BUT also sold as Toasted Oats ® under in- house labels in 39 grocery stores All cases had consumed a common cereal

16. Product Identification Is Not Enough Most outbreaks are due to a temporary problem in production chain Knowing a brand name is not enough, you also need: Item description Place, date of purchase Manufacturer, supplier and lot number Locations of farms, production facilities, supplier information, delivery schedules

17. Getting Started For a traceback investigation information is collected from: Cases Retailers or point of service establishments Distributors/importers Producers/processors

18. Traceback: First Steps Begin with information available from interviews of the cases about the time and place of purchase of implicated item Original packaging and labels with identifying features (lot numbers, names of manufacturers) are helpful

19. Traceback: Next Steps Continue investigation at place(s) where cases obtained items such as retail stores or restaurants Expand investigation to distributors Includes brokers and importers and may have multiple levels Business documentation (invoices, inventory records, air bills, bills of lading) and customs forms can be helpful

20. Traceback: Final Steps A traceback investigation is completed when firms that supplied, processed and produced the implicated product are identified Investigation may include a visit to the source to verify information collected (production dates, locations of farms/facilities) Validity of a traceback investigation is highly dependent on proper documentation Missing documentation (such as receipts or labels) makes the investigator’s job difficult

21. To Trace or Not to Trace? Tracebacks can be time consuming While important, such investigations should be undertaken selectively Criteria for undertaking a traceback: Certainty that the vehicle in question is truly implicated in the outbreak AND that The source of the contamination is within the production chain

22. To Trace or Not to Trace? Other key questions to consider: Is there solid epidemiologic evidence linking the outbreak and the implicated products? Is there historical precedent for the product being contaminated with the organism in question? Is there microbiological evidence linking the outbreak and the implicated products?

23. To Trace or Not to Trace? Key questions, continued: Does the vehicle have chemical and physical characteristics conducive to the survival and growth of the causative agent? Has mishandling or environmental contamination of the product by the consumer, retailer or point of service establishment been ruled out? Could the product be commercially distributed in a way that is consistent with the outbreak?

24. To Trace or Not to Trace? Another factor to consider is the likelihood of success Tracebacks are most successful with: Commercially packaged products (identifying label) Unusual products (salami) Products with a long shelf-life (frozen hamburger) Traceback investigations are unproductive with: Products with a short shelf-life (fresh fruits and vegetables) Products derived from multiple sources (blood clotting factor from multiple donors)

25. To Trace or Not to Trace? Weigh benefits of the investigation How serious is the disease? Death, hospitalization or permanent disability? Is exposure likely to be ongoing? Are vulnerable populations at risk? Infants, elderly, immunocompromised persons? A “yes” to any/all of these questions might provide justification to undertake a traceback investigation

26. Success Factors Coordination among many players Local, state or federal agencies Good solid epidemiological data Poor epidemiologic studies might implicate the wrong vehicle and misdirect the investigation Information obtained from epidemiological investigation about the vehicle is often the first step in the traceback investigation

27. Conclusion To trace the source of an outbreak you need to look back in time Use a traceback investigation as a first step in determining where problems may have occurred in the chain of production of an implicated vehicle Traceback investigations provide data for the next step: the environmental health assessment

28. References 1.Hennessy TW, Hedberg CW, Slutsker L, et al. A national outbreak of Salmonella Enteritidis infections from ice cream. N Engl J Med. 1996;334:1281-1286. 2.Breuer T, Benkel DH, Shapiro RL, et al. A multistate outbreak of Escherichia coli O157:H57 linked to alfalfa sprouts grown from contaminated seeds. Emerg Infect Dis. 2001;7:977-982. 3. CDC. Multistate outbreak of Salmonella Serotype Agona infections linked to Toasted Oats cereal—United States, April-May, 1998. MMWR Morb Mortal Wkly Rep. 1998;47:462-464.