Maple Leaf Foods has recalled all products that were manufactured at its Toronto plant, after the facility was linked to a listeria outbreak that killed four people.

Up to 220 products are now involved in the expanded recall. But Maple Leaf CEO Michael McCain said the expansion is only a precautionary measure and none of the products added to the recall on Sunday have shown any trace of listeria.

The company is warning consumers not to serve or eat meat products labelled with establishment number 97B. Customers can find the number near the "best before" label or packaged on dates.

Three people have died in Ontario and one person in British Columbia because of the outbreak. There have been at least 21 confirmed cases in total.

The disease has an incubation period of up to 70 days, meaning there could be more cases in the weeks ahead, according to Dr. Mark Raizenne of the Public Health Agency of Canada.

Despite the four deaths, Health Minister Tony Clement said authorities acted quickly to warn Canadians about the outbreak and called it a "success."

Ontario health officials know about some listeria cases in July, but it was not until last week that any products were recalled.

"These products have been distributed nationally to retail stores and food service institutions such as restaurants, hospitals, nursing homes, and other institutional cafeterias or kitchens," Maple Leaf Foods said in a news release.

"These products may also be sold at deli counters. If the original product identity and best before code is not evident, consumers are advised to check with their retailer to determine if the product is included in the list of recalled products."

The company was compelled to issue the recall after tests indicated the plant is the source of the listeria bacteria. The plant has been temporarily shut down and is now being sanitized.

"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 Saturday in a statement.

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

Patients contract listeriosis after consuming foods contaminated with listeria monocytogenes.

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."

Maple Leaf began recalling products last week when initial tests showed two types of meat contained the bacteria. That list expanded to 23 products earlier this week. On Saturday, several types of packaged sandwiches were also recalled.

Public health officials have warned that food contaminated with listeria may not look or smell like it has spoiled.

Listeriosis can cause flu-like symptoms, such as a stiff neck, headache, nausea and fever. Healthy individuals may remain symptom-free. However, pregnant women, the elderly and people with weakened immune systems are at greatest risk.

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.