Public health officials in Canada said they have linked a deadly bacterial outbreak that killed four people to recalled meat products from Maple Leaf Foods.

The outbreak has resulted in 21 confirmed cases of listeriosis, a kind of food poisoning that can be dangerous to the elderly, newborns, pregnant women and people with chronic medical conditions. Symptoms include fever, headache, stiffness, nausea, abdominal pain and diarrhea.

"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. Test results for the third product were a close match to the outbreak strain, but showed a slight variance, the agency added.

The recall is expected to cost more than $19 million as Maple Leaf expanded its recall Sunday to include more than 220 of its products.

Still, the investigation into the cause of the outbreak is far from complete, the agency said.

Maple Leaf's Toronto plant has shut down temporarily to allow for heavy sanitizing of the facility.

Linda Smith, a spokesperson for Maple Leaf, said all the recalled meat products had been removed from stores shelves across Canada by Thursday.

However, determining where the products ended up after they were purchased by distributors — such as in hospitals or retirement homes — has been more complex.

"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.

An additional 30 suspected cases are being probed to confirm if they are related to the outbreak. Officials have said they expect to see more cases crop up, given that listeriosis has an average incubation period of three weeks.