Trace Back Investigations

When individuals become ill, and suspicion falls on the food supply, governmental public health initiate a trace-back investigation, which enlists the assistance of food suppliers. As discussed in Chapter 3, trace-back investigations involve tracing a product by using shipping and purchase records at each link in the distribution chain back to common points that can explain the occurrence of illness among all or most affected individuals. Governmental public health regulations vary by jurisdiction and can provide the legal basis for trace-backs within state lines; however, in many cases, the FDA and CDC may become involved. Trace-back by the FDA involves numerous challenges, including the absence of records, the inability to require that records be maintained or provided, the existence of multiple sources of product and complex distribution systems, and the resource-intensive nature of the process, which may or may not confirm a contamination.

When consumers fall ill after eating food purchased from a retailer or restaurant, investigators will elicit a food consumption history, as well as the restaurants or retailers they patronized. The retailers or restaurants, in turn, identify the wholesalers. The wholesalers identify their suppliers, who may have difficulty identifying the farm or farms of origin because of product commingling. (The commingling of farm products is a major gap in trace-back ability.) At each point in the trace-back, inspectors observe the procedures for storing or processing the food, looking for abuses that would result in food contamination. Specimens may be taken to determine if other similarly handled food or the environment that the food was stored or processed in is contaminated. If there is evidence to suggest that contaminated food is in the distribution chain, then the manufacturer initiates a recall of that food.

Before recent molecular advances in laboratory techniques, it was not possible to know that two or more individuals who have never met and have no obvious exposure in common were, in fact, infected with the same rare strain of a virus or bacteria. With the advent of the new technology, it becomes possible to conduct case-control interviews and to determine that there is a common exposure to the same type of produce or food product. Figure 3.11 (Chapter 3) is a diagram from a FDA manual on trace-back. In this hypothetical trace-back, contaminated food infected individuals at four different point-of-service locations in different states. The trace-back allowed investigators to identify a single farm. Before these recent laboratory advancements, we would not even know that the four point-of-services events were related. Recent laws make it even easier to do trace-back, since food distributors are now required to maintain trace-back information.

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