Farms Pacific may have been a little too quick to recall its diced celery and onion blend over the Thanksgiving weekend. The latest U.S. Food and Drug Administration (FDA) testing has been unable to confirm E. coli in the product. As of Nov. 23, 19 people have been infected with E. coli O157:H7, and epidemiological evidence suggests that rotisserie chicken salad made and sold at Costco Wholesale stores in several states was a likely source of the outbreak. Preliminary testing of a sample of diced celery and onion blend collected from a Costco location by the Montana Public Health Laboratory indicated the presence of E. coli O157:H7. The blend was used to make the rotisserie chicken salad eaten by outbreak victims. It was supplied by Taylor Farms Pacific, which voluntarily recalled multiple products containing celery from retailers such as Costco, Starbucks and Target. However, an investigation update provided by the U.S. Centers for Disease Control and Prevention (CDC) on Dec. 8 stated that further laboratory analysis was unable to confirm the presence of E. coli O157:H7 in the sample of diced celery and onion blend produced by Taylor Farms Pacific. The preliminary test performed on the sample was a polymerase chain reaction (PCR) test, which is commonly used to rapidly screen for the presence of bacterial DNA. The diced celery and onion blend has not been ruled out as a source of the outbreak, and investigators are continuing to work to identify which ingredient in the chicken salad is linked to the illnesses. (To sign up for a free subscription to Food Safety News, click here.)