With 19 sick from E. coli O157 linked to Costco rotisserie chicken salad, investigators are looking at ingredients for the original source.

On Nov. 26, a celery and onion mix was identified leading to an expanded recall this week of 155,000 items, including salad kits, vegetable trays and other prepared foods. The products were sold at chains across the country, including Walmart, Costco, 7-Eleven and Target.

Costco says it uses one supplier for vegetables in the chicken salad sold in all its U.S. stores.

But Bruce Taylor, chairman and chief executive officer of Salinas-based Taylor Farms told the Monterey Herald federal and state officials are jumping the gun in linking the E. coli to celery processed by Taylor Farms Pacific, and that the recall was based only on “an abundance of caution.”

Taylor said Montana health officials, where the outbreak was first reported, generated a “presumptive positive,” meaning they identified the strain of E. coli O157:H7 from samples taken from sick consumers as the same strain found on Taylor Farms celery products. However, it hasn’t been determined yet if it’s exactly the same bacteria. A positive match can only be made when DNA testing is complete.

“Since the state of Montana’s initial preliminary findings, the state lab has not been able to confirm the existence of E. coli in their sample and has not been able to gain any information or link,” Taylor said. “Normally, this would take three or four days, which would have been last Saturday or Sunday, for results. Today, it looks like a false alarm.”

But the Centers for Disease Control and Prevention said in a statement that “preliminary laboratory evidence indicates that a celery and onion diced blend produced by Taylor Farms Pacific Inc. may be contaminated with E. coli O157:H7. This product was used to make the Costco rotisserie chicken salad eaten by ill people in this outbreak.

Taylor Farms contracts with hundreds of growers from Salinas to Mexico to supply produce.

For a complete list of recalled products, visit the U.S. Food and Drug Administration website: www.fda.gov/Safety/Recalls.