Costco, Walmart, Kroger and other retailers are pulling romaine lettuce products off their shelves in response to warnings from federal investigators about the nationwide E. coli outbreak blamed on contaminated romaine.

The E.coli outbreak stems from chopped romaine lettuce originating in Yuma, Ariz., according to the Centers for Disease Control and Prevention. The vast majority of romaine grown between November and March is from there. The CDC advised consumers to avoid packaged romaine that comes from the Yuma area.

“We pulled every salad product that came from Yuma, or even had the potential to come from Yuma,” says Craig Wilson, vice president of quality assurance and food safety at Costco. “I think everyone is focused on following the advice we were given.”

Meanwhile, Panera Bread, which is being sued by a New Jersey woman who allegedly contracted E. coli there in March, announced that it switched its romaine provider. (Panera didn’t respond to a request for comment on the lawsuit.)

The moves follow an earlier decision by Fresh Foods Manufacturing of Pennsylvania, which packages grab-and-go salads for supermarkets and convenience stores, to issue a voluntary recall of roughly four and a half tons of pre-packaged salads and lettuce mixes.

But Consumer Reports says it’s unrealistic to expect consumers to figure out whether their romaine was produced in Arizona. As a result, CR is advising people to avoid all romaine lettuce sold in stores and restaurants along with bagged romaine lettuce mixes and prepared salads. This advice includes whole-leaf romaine, in an abundance of caution.

Consumer Reports is also now advising people to avoid pre-made salads and bagged lettuce mixes that don’t specifically name the lettuces they contain. For example, products labeled “Spring Mix” or “Asian Lettuce Blend” may not list all the greens inside…