Investigators face difficulty in tracking E. coli outbreak linked to romaine lettuce

Consumer Reports is urging people not to eat romaine lettuce until the source of E. coli contamination is found.

In a statement the Centers for Disease Control said, "Because we have not identified a source of the infections, CDC is unable to recommend whether U.S. residents should avoid a particular food."

"When you have a situation like this the public obviously wants answers but it can be a very difficult process to trace down," said Deputy AG Commissioner Melissa Cregan.

Fresno County Deputy AG Commissioner Melissa Cregan says finding the E. coli source in this case is very difficult because samples may no longer exist.

"Particularly right now when you look at the last instance being almost a month ago right now. This is very perishable product. It's most likely not in grocery shelves or necessarily in homes at this point," said Ryan Jacobsen.

Canadian authorities have urged people in five provinces to throw out any romaine lettuce they may have.

"The CDC I think is still looking at this as being mostly a Canadian problem. Does that mean this was something produced in Canada? Quite possibly," said Cregan.

RELATED: 1 dead, dozens sickened after romaine lettuce E. coli outbreak in United States

Fresno County has two lettuce seasons. The fall season wrapped up in November.

Canadian investigators linked romaine lettuce to the outbreak but they have not able to trace the cause of contamination.

"Whatever might have been the potential problem on this one whether it's US or foreign born, at this time it's probably gonna be some time before they really find it because of the length of time that's passed already," said Jacobsen.

Consumers can help protect themselves against an E. coli infection by taking simple steps.

"Wash your hands, wash your produce. Cook all your foods to the appropriate temperature," said Cregan.