SEATTLE (AP) — 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.

• REVISED: 19 people in 7 states ill in E. coli outbreak tied to Costco, November 26, 2015

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.

Phone calls to the company did not get answered on Wednesday afternoon. A message left with the FDA was not immediately returned.