If you have a warehouse membership card in your wallet or a supermarket shopper tag on your key chain, you might regard it as a good way to save money. But public health officials say it may be an even better way to save lives.

JoNel Aleccia of NBC News reports that more local health departments — along with state and federal investigators — are relying on the detailed information about what went in consumers’ shopping carts to track down outbreaks of foodborne illness, experts say.

Identifying exactly which products were purchased by victims of food poisoning has become a standard tool for public health investigators, said officials with the Centers for Disease Control and Prevention.

“We are definitely supportive of the use of shopper cards during these outbreak investigations,” said Casey Barton Behravesh, deputy chief of the CDC’s outbreak and prevention branch of the division of foodborne, waterborne and environmental diseases. “The product, the flavor, the lot code, the best by date: That is all tracked with these purchases.”

Store cards are a rich trove for epidemiologists, who often are trying to track down suspect food a month or so after it was consumed because of the lag between when an illness strikes and when it gets reported, said Bill Keene, a senior epidemiologist with the Oregon Public Health Division. His state has been a leader in using shopper card data, along with Minnesota, but others are joining in, Keene said. 

“We rely on people’s memories, which are quite fallible, and on our interviews, which are quite fallible,” Keene told NBC News. “Shopper club cards are a good source of finding out what people ate.”

Costco has been notifying consumers about food and other products recalls for safety reasons since the late 1990s, said Craig Wilson, the company’s vice president for food safety and quality assurance. But now, they’re being called on by public health officials at every level.

“It happens a couple times a week,” said Wilson. “It’s getting to be more of a norm.”

But it’s not always easy, Keene says. Stores provide data only with the permission — usually written consent — of the consumer and a verified shopper card or membership number. And disclosure rules vary from state to state, making some information more difficult to obtain.

“We won’t just release data,” said Wilson.

Health officials like Keene say they safeguard the data carefully and use it only as a tool to keep more people from getting sick.

“We are the government, but we aren’t that part of the government,” he said. “We’re the good guys.”