The shopper cards issued by supermarkets and warehouse stores do more than provide access to discounts, they also allow stores to record the purchases each customer makes. Retailers have long envisioned using their vast purchase databases as marketing tools, potentially targeting messages to individual customers based on their shopping patterns. Public-health officials now see another application of purchase data – identifying food-safety hazards and preventing widespread outbreaks of food-borne illness.

According to a report from NBC News, the U.S. Centers for Disease Control and Prevention (CDC) and some state health departments have used shopper-card data to identify exactly which foods a patient purchased and ate. They then can cross-reference the list with those from other patients and identify the source of food-borne illness. Once the source is confirmed, officials can pull the product from shelves and send warnings directly to other customers who purchased the product, again using shopper-card data. Normally, health officials rely on interviews with patients to track down sources of food-borne illness, but the process is slow and can be unreliable.

The article notes that privacy issues are a concern. Grocery chains generally release the shopper-card information only with permission of customers, and disclosure laws vary between states, so the availability of the information to health officials varies from one case to another. About 60 percent of U.S. grocery stores offer shopper cards and about 80 percent of U.S. consumers belong to at least one food-store loyalty program.