Source: The Canadian Press | Associated Press

TORONTO - The Canadian Food Inspection Agency says it hasn't been able to find the source of E.coli contamination which led to the recall of burgers made by an Ontario company.

The CFIA says it has completed its investigation into ingredients used in burgers produced at Cardinal Meat Specialists Ltd., which is based in Brampton, Ont.

Certain batches of burgers produced by the company were linked to an E.coli outbreak in mid-December which sickened five people.

The food inspection agency says after "extensive efforts," there is no evidence available to pinpoint a source of the contamination.

It says its investigation looked at spices, domestic beef ingredients and international beef ingredients.

Investigators assessed production, inspection and testing records, reviewed plant food safety procedures and conducted additional testing on burger ingredients.

The CFIA says all available domestic beef ingredient products tested negative for the E.coli strain related to the recalled burgers.

All spices also tested negative for E.coli and were ruled out of the investigation.

Additionally, investigators found all international ingredients in the burgers met all import certification and testing requirements. The CFIA also said there were no reported cases of illnesses in those countries related to the same E.coli strain.

"As all lines of inquiry have been exhausted, the CFIA's investigation will not progress further," the agency said in a statement.

"Canada has rigorous requirements for meat production to reduce the risk of E. coli, but even the best food safety systems cannot eliminate all potential opportunities for contamination all the time."

The CFIA says it will continue to work with public health authorities to monitor any reported cases of illness.

It advised consumers to keep their food safe by cooking ground beef thoroughly to destroy E.coli bacteria, and by ensuring that cooking surfaces and utensils are well cleaned after handling raw beef.

Five people — three in Alberta and two in Ontario — became sick after eating Butcher's Choice brand frozen beef burgers.

Two other beef products — Cardinal Select brand Prime Rib Beef Burgers and Butcher's Choice Hickory Barbecue Beef Burgers — were also recalled, but they were not linked to any cases of illness.

All the products, which were recalled between Dec. 12 and Dec. 15, were produced by Cardinal Meat Specialists and had been sold at Loblaws stores across Canada.