A multistate outbreak of E. coli infections tied to walnuts has sickened at least a dozen people, seven of whom have been hospitalized. 

The Food and Drug Administration (FDA) is working with the Centers for Disease Control and Prevention (CDC) and local health officials to investigate the outbreak of infections that have been linked to organic walnuts from Gibson Farms Inc. of Hollister, California. 

The walnuts were distributed in bulk bins to multiple natural food and co-op stores in over a dozen states. However, officials said that some stores may have repackaged the bulk walnut halves and pieces into plastic clamshells or bags. 

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About 10 people have been interviewed by state and local health officials. 

All of them confirmed that they ate walnuts in the week before becoming ill, the FDA said. Additionally, almost all of them reported buying organic walnuts from bulk bins in food co-ops or natural food stores, federal health officials continued. 

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The FDA has a seven-page list of all the impacted stores, including certain Whole Foods Market locations, posted on its website.

FOX Business' reached out to Whole Foods for comment.

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After the FDA’s traceback investigation identified Gibson Farms Inc. as the common supplier of walnuts in this outbreak, the company issued a voluntary recall at the end of April.

Aside from the recall, Gibson Farms also contacted their distributing customers.

The FDA is still working with the company and its distributors to determine the source of the contamination. Federal officials are also trying to determine whether other products or states have been impacted. 

The FDA said it will update the advisory when it receives more information.