Environmental Health Investigations: Conducting Traceback Investigations.
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Transcript of Environmental Health Investigations: Conducting Traceback Investigations.
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Getting Started
For a traceback investigation information is collected from: Cases Retailers or point of service
establishments Distributors/importers Producers/processors
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
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
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
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
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?
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?
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)
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
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
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
References1. 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.