(CNN) -- Canadian health officials have linked a deadly listeriosis outbreak to a Maple Leaf Foods plant in Toronto, prompting the company to expand of its recall of meat products.
The bacterium is typically found in herd animals, meats, unpasteurized milk and unprocessed cheese.
Four people have died from a strain of listeriosis that has been linked to the meat plant, while another 21 people have confirmed cases of the bacterium, Canada's Public Health Agency said Saturday. Thirty other cases are under investigation, the agency said.
Maple Leaf Foods of Ontario immediately widened the recall of all foods processed out of its Bartor Road facility after the announcement Saturday by Canadian health officials.
"Because the onset of symptoms of listeriosis can occur up to 70 days after contaminated food is consumed, it is expected that the number of confirmed and suspected cases will continue to increase over the next several weeks," the Public Health Agency said in its Saturday statement.
Last week, Maple Leaf Foods said it was recalling products "as a precautionary measure" and temporarily closing its Bartor Road, Toronto, plant after "a small number" of its meat products tested positive for the bacteria.
"Tragically, our products have been linked to illness and loss of life," Maple Leaf Foods CEO Michael McCain said in a statement released Saturday. "To those people who are ill, and to the families who have lost loved ones, I offer my deepest and sincerest sympathies."
The outbreak was first noted last month, when routine surveillance detected an increase in cases reported by Ontario public health units, Dr. David Williams, the province's acting chief medical officer of health, told reporters last week.
The rare but potentially serious foodborne illness is most dangerous among the elderly, pregnant women and people with depressed immune systems, he said.
Maple Leaf Foods was named last week as the probable source of the tainted meats. The company was distributing its products to food service institutions, restaurants, hospitals and nursing homes, according to Williams.
A complete list of the suspect products is available at the Canadian Food Inspection Agency Web site. Williams advised the public not to eat any ready-to-eat meats whose source is not identifiable.
The confirmed listeriosis cases are in four Canadian provinces, and Canadian doctors have been ordered to be on the alert for possible cases, Williams said.
The bacterium is typically found in herd animals, meats, unpasteurized milk and unprocessed cheese products. Treatment usually includes a course of antibiotics.
People with listeriosis can have fever, muscle aches and sometimes nausea or diarrhea, according to the U.S. Centers for Disease Control and Prevention.
If the infection spreads to the nervous system, it can result in headache, stiff neck, confusion, loss of balance or convulsions, it said.