The US Centres for Disease Control and Prevention (CDC) said Costo's rotisserie chicken salad has been linked to 19 cases of E. coli.
The agency said it was still not sure which ingredient was the cause of the outbreak.
Costco said it stopped selling the chicken salad on 20 November, when it was notified of the outbreak.
This particular strain of the disease can be life-threatening, but no deaths have been reported.
According to the CDC, five people have been taken to hospital and two have reported kidney failure.
Incidents of the outbreak have been reported in Montana, Utah, Colorado, California, Missouri, Virginia and Washington.
Officials this month linked an outbreak of E. coli to food served at branches of Mexican fast food chain Chipotle in Washington, Oregon, California, Ohio, New York and Minnesota.
Wholesale outlet Costco is the latest retailer to be linked to an outbreak of E. coli.