Environmental Health Investigations: Conducting Traceback Investigations

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.