Many people own a shopping card for large grocery stores—those little plastic cards that provide coupons based on previous purchases and track overall savings. Now they could also help identify the source of a food-related disease outbreak.

Salmonella is a form of bacteria that can cause food poisoning and can be picked up from contaminated food. A recent outbreak struck 250 people in 44 states, according to the Centers for Disease Control and Prevention Web site.

While trying to trace the origin of the foodborne outbreak, the CDC tried using shopper-card data to examine grocery purchases and look for common items that may have been tainted.

Permission from patients in Washington state who used shopping cards granted the CDC and workers from the Washington State Health Department access to their buying records, said Laura Bettencourt, epidemic intelligence officer for the Division of Foodborne, Bacterial and Mycotic Diseases at the CDC. Other states have followed suit.

“We’ve tried to use shopper cards in the past during outbreak investigations,” Bettencourt said. “We had success using them during the nationwide outbreak of salmonella linked to salami products that contained contaminated pepper.”

The clue came from data collected in Washington, she said. With more than 500 pages of information to leaf through, health department workers were able to identify a single brand purchased in five of the seven state cases.

“It was pretty exciting for us,” Bettencourt said. “We will definitely use [this technique] in the future.”

According to Bettencourt, future investigations would benefit by gathering information from each household member.  Since every member can have a unique shopper identification number, it is important to collect the data from each individual.

Alfred Rademaker, professor in the Department of Preventive Medicine at Northwestern University, said the cards could be very helpful in understanding outbreaks and locating their source, but he questions investigations similar to the salmonella outbreak.

“I have to think [about] where the holes are in the technique,” Rademaker said.

There are potential sampling problems because there are many people who don’t use their shopping cards or patronize stores that use them, he said.

However, the difference in the usefulness of the data may only be marginal because of the ability to generalize data. He also dismissed the claim of some consumer groups that the cards are an invasion of privacy and said getting permission is still the “gold standard,” and that it is conceivable to think of using a card as tacit permission.

“We’re getting into a time when this stuff is going to explode whether we like it or not,” Rademaker said. “The stores have these cards, whether you use the data or not.”

Leila Maloff, a senior journalism major at Columbia, said she uses a shopper card and sees the potential benefit from allowing the CDC or a health department access to the data. She said as a consumer, she does not feel her privacy is infringed by allowing access to the data and understands the potential benefits.

“I don’t really care if someone knows I buy canned soup instead of vegetables,” Maloff said.

She echoed Bettencourt’s concern in getting proper data from within households. Often, people will share a shopper card or use a friend’s.  Maloff doesn’t even remember who the card she uses was initially issued to.  This can make it difficult to contact the correct person when contaminated food is identified.

Bettencourt said while the capabilities of shopper cards are becoming apparent, she does not foresee the use of cards ever becoming mandatory.  She also stressed the importance of consumers knowing the data would never be accessible without an individual’s consent.

“We have to get the shopper numbers from customers,” she said. “The records are very confidential, like medical records.”