Lettuce. (REUTERS FILE/Michael Buholzer)

Health officials have determined a recent E. coli outbreak in Nova Scotia, New Brunswick and Ontario comes from tainted lettuce at Taco Bell and KFC restaurants.

Nova Scotia health officials said Friday the contaminated vegetable should no longer be in distribution.

"Lettuce has a limited shelf life, and we have not seen a new case in more than a week. This tells us it is highly unlikely the food item remains in the food chain. As an added precaution, the Canadian Food Inspection Agency is issuing a recall of the lettuce products," Dr. Frank Atherton, Nova Scotia's deputy chief medical officer of health, said in a press release.

Five of 10 E. coli cases in Nova Scotia during this period have been linked to the contaminated lettuce, the press release said, adding the impacted locations have been inspected and don't have any of the affected product.

Six cases in New Brunswick and 10 cases in Ontario are believed to be linked.