A retailer or food service operator is only as good as the ingredients they use. Even with the best internal food safety programs, a good food safety culture includes supplier standards and verifications. Audits and inspections are never enough.

According to the Associated Press, Costco believes that contamination of their rotisserie chicken salad is linked to produce.

Costco officials say testing has pointed toward a vegetable mix from a California food wholesaler as the source of E. coli in the company’s chicken salad that has been linked to an outbreak that has sickened 19 people in seven states.

Craig Wilson, Costco vice president of food safety and quality assurance, said Wednesday he was told by the Food and Drug Administration that the strain of E. coli seems to be connected to an onion and celery mix.

Wilson says the company uses one supplier for those vegetables in the chicken salad sold in all its U.S. stores.

He says one additional test is needed to confirm that the vegetables carried the same E. coli strain connected with the outbreak.

Wilson identified the supplier as Taylor Farms in Salinas, California.