environmental health investigations: conducting traceback investigations

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.