Test results indicate a Maple Leaf Foods plant in Toronto is the source of a Listeria outbreak that has killed four people, public health officials confirmed late Saturday. The company plans to recall all products produced at the facility as a precaution.

"Results of genetic testing from three samples of the products recalled by Maple Leaf Foods show that two tested positive for the outbreak strain of listeria," the Public Health Agency of Canada said in a statement.

The third sample was a close match to the outbreak strain and is undergoing another test.

There have been 21 confirmed cases of listeriosis across the country. Three people have died in Ontario and one in British Columbia.

Michael McCain, CEO of Maple Leaf Foods, gave his "deepest and sincere condolences" on Saturday to the families of those who died.

"This week, our best efforts failed and for that we are deeply sorry," McCain told reporters. "This is the toughest situation we've faced in the 100 years of this company's history."

Although the company plans to recall all products made at the Toronto plant on Sunday morning, he said it was a precautionary measure and no trace of listeriosis had been found on any products not already pulled from the shelves.

The plant has been temporarily shut down. Company spokesperson Linda Smith said all of its previously recalled meat products had been taken off store shelves by Thursday. However, finding out where products ended up after being purchased by distributors had proven to be more difficult.

"There is a very active effort to work with all the food distribution customers. But it is not as direct, because there are customers, and then those customers have customers," she said.

"We are very confident, but I can not give you a percentage, but virtually all of it has been removed."

Federal Agriculture Minister Gerry Ritz said Saturday he is confident that health officials will quickly get the outbreak under control.

"I mean we always have these types of situations," Ritz told CTV News on Saturday. "There have been outbreaks like this before. We are getting better at what we do."

Meanwhile, consumers in Toronto are being warned not to eat Shopsy's deli-fresh Classic Reuben sandwiches over contamination fears.

The sandwiches are sold in 180-gram packages. They have best-before dates of up to and including Aug. 22 and 24. The UPC code is 7-76393017001-8.

CFIA initiated the recall because the sandwich contains sliced corned beef -- one of the deli meat products recalled by Maple Leaf Foods earlier this month.

The sandwiches were sold at a number of locations in Toronto. The CFIA and Royal Touch Foods list the following locations:

• Shoppers Drug Mart 390 Queens Quay
• Shoppers Drug Mart, 388 King Street West
• Shoppers Drug Mart 10 Dundas Street
• Shoppers Drug Mart, 465 Yonge Street
• Shoppers Drug Mart, 4990 Yonge Street
• Shoppers Drug Mart 5776 Yonge Street
• Bloor Superfresh Mart, 186 Bloor Street

"My understanding is there were 96 sandwiches produced and 23 sandwiches are outstanding, which I think speaks to the level of detail that everybody is going to to get the product back," Maple Leaf spokesperson Linda Smith told CTV Toronto on Saturday.

There have been no illnesses reported yet in association with consumption of the sandwiches. Generally speaking, eating Listeria-tainted food can lead to high fever, severe headache, neck stiffness and nausea.

In some rare cases, people can die, but those most at risk are the elderly and those with health problems.

A recall of Maple Leaf products began last weekend. The company recalled 23 packaged meat products, including sliced cooked turkey breast, roast beef and salami. All were processed at a plant in Toronto -- specifically, two production lines.

The products that are part of the recall have been distributed to nursing homes, delis and restaurants across Canada, including McDonald's and Mr. Sub.

Maple Leaf had closed its plant earlier this week. Decontamination efforts continued at the plant Saturday.

With a report from CTV's Graham Richardson and CTV Toronto's Chris Eby

Here is the current list of affected products, including individual product codes and best-before dates:

• 26365, Sliced Cooked Turkey Breast, 470 grams, Sept. 30;
• 02106, Schneiders Bavarian Smokies, 1 kilogram, Oct. 28;
• 02126, Schneiders Cheddar Smokies, 1 kilogram, Oct. 28;
• 21333, Sure Slice Roast Beef, 1 kilogram, Sept. 30;
• 21388, Sure Slice Combo Pack, 1 kilogram, Sept. 30;
• 60243, Deli Gourmet Roast Beef slices, 1 kilogram, Sept. 30;
• 02356, Seasoned Cooked Roast Beef, 500 grams, Oct. 7;
• 42706, Roast Beef, Seasoned and Cooked, 500 grams, Oct. 7;
• 21334, Sure Slice Turkey Breast Roast, 1 kilogram, Oct. 14;
• 21444, Sure Slice Corned Beef, 1 kilogram, Oct. 14;
• 44938, Montreal Style Corned Beef, 500 grams, Oct. 14;
• 21440, Sure Slice Black Forest Style Ham, 1 kilogram, Oct. 21;
• 21447, Sure Slice Salami, 1 kilogram, Oct. 21;
• 21331, Sure Slice Smoked Ham, 1 kilogram, Oct. 21;
• 48019, Schneiders Deli Shaved Corned Beef, 200 grams, Oct. 21;
• 48020, Schneiders Deli Shaved Smoked Meat, 200 grams, Oct. 21;
• 48016, Schneiders Deli Shaved Smoked Ham , 200 grams, Oct. 21;
• 48018, Schneiders Deli Shaved Smoked Turkey Breast, 150 grams, Oct. 21;
• 48017, Schneiders Deli Shaved Fully Cooked Smoked Honey Ham, 200 grams, Oct. 21;
• 21360, Burns Bites Pepperoni, 500 grams, Jan. 21, 2009;
• 99158, Turkey Breast Roast, 1 kilogram, Sept. 30;
• 71330, Roast Beef Cooked, Seasoned, 2.5 kilograms, Sept. 30;
• 71331 Corned Beef, Smoked Meat, 2.5 kilograms, Sept. 30.