Health officials have determined an E. coli outbreak that left 19 people ill was traced to a celery-and-onion mix used in Costco Wholesale's chicken salad. The California-based maker of the diced vegetable mix, Taylor Farms Pacific Inc., issued a recall on the Food and Drug Administration website on Thursday. Montana state health authorities said the blend tested positive for the E. coli strain, which can be deadly and cause serious gastrointestinal illness. At least five of the 19 people who were sick were hospitalized, but no deaths have been reported. The outbreak was reported in Montana, Utah, Colorado, California, Missouri, Virginia and Washington state, according to the federal Centers for Disease Control and Prevention.