CHAMPAIGN, ILL. ? As they scrambled recently to trace the source of a salmonella outbreak that has sickened hundreds around the country, investigators from the Centers for Disease Control and Prevention successfully used a new tool for the first time — the shopper cards that millions of Americans swipe every time they buy groceries.

With permission from the patients, investigators followed the trail of grocery purchases to a Rhode Island company that makes salami, then zeroed in on the pepper used to season the meat.

Never before had the CDC successfully mined the mountain of data that supermarket chains compile.

“It was really exciting. It was a break in the investigation for sure,” CDC epidemiologist Casey Barton Behravesh said.

At least 245 people in 44 states have been sickened in the outbreak. That includes 30 in California, 19 in Illinois, 18 in New York and 17 in Washington state.

Shopper cards have been around for more than a decade, offering customers discounts in exchange for letting supermarkets track their buying habits. The cards are used to build customer loyalty and help stores market their products.

The first case in this salmonella outbreak was reported last summer, and by November, CDC investigators were examining a multistate cluster of cases.

Through interviews and questionnaires, investigators suspected some kind of Italian meat was the culprit, but people couldn’t remember what brand they bought, Behravesh said.

So the CDC asked supermarkets for certain buying information on seven victims in Washington state, focusing on suspect products rather than everything the customers had bought, Behravesh said. “We didn’t care about the brand of toilet paper people were buying,” she said.

Of those seven people, five had bought Italian meats made by the Rhode Island company, Daniele International Inc., Behravesh said.