At least they seem to have found the problem quickly….

Testing has pointed toward a vegetable mix from a California food wholesaler as the source of E. coli in Costco chicken salad that has been linked to an outbreak that has sickened 19 people in seven states, a Costco official said Wednesday.

Craig Wilson, Costco vice president of food safety and quality assurance, said 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.

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

One additional test is needed to confirm that the vegetables carried the same E. coli strain connected with the outbreak, he said.

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.

The number of people sickened in the outbreak will likely grow over the next few weeks, even though the product has been removed from store shelves, the federal Centers for Disease Control and Prevention said earlier in the day.

The spread of foodborne illness takes time to track, especially when it’s happening in multiple states, said Dr. Robert Tauxe, deputy director of the CDC’s Division of Foodborne, Waterborne and Environmental Diseases.

State health officials, particularly those in Utah, discovered the outbreak and helped find links between the 19 illnesses in seven states, Tauxe said.

“Very quickly they noticed these people did have something in common. They really liked and ate the rotisserie chicken salad,” he said.

The big-box retailer based in Issaquah, Washington, pulled the chicken salad off store shelves nationwide, posted signs in its stores and provided detailed purchase logs to the CDC to help it track who bought the product and where the salad ingredients came from, Tauxe said.

Costco is working closely with the CDC, FDA and local health officials to find the source of the E. coli and has encouraged its suppliers to do the same, Wilson said.

“We feel terrible about the people who got sick,” he said.

The strain of Shiga toxin-producing E. coli can be life-threatening, but no deaths have been reported. Five people have been hospitalized, including two with kidney failure. The CDC has been told they are all getting better, Tauxe said.