A Saskatchewan woman who was the province's single confirmed case of listeriosis has died, the provincial government said Tuesday.

The elderly woman, who was living in a long-term-care facility in the Heartland health region southwest of Saskatoon, died on Sunday. She tested positive for the same strain of listeria bacteria found in a Maple Leaf meat processing plant in Ontario that has been linked to other listeriosis cases.

Public health officials are continuing to investigate whether listeriosis caused her death or was a contributing factor in her death, said Dr. Johnmark Opondo, acting provincial deputy medical health officer.

"This is a woman who has other medical illnesses," Opondo said. "This woman has been unwell, from what I understand, almost 20 years."

Across Canada, 15 people carrying the Listeria monocytogenes strain that was found in the Maple Leaf foods plant have died. The strain was the underlying or contributing factor in six of those 15 fatalities, while the deaths of the other nine patients who had the bacterium in their system are still under investigation to determine the exact cause, the Public Health Agency of Canada said.

Saskatchewan has two other suspected listeriosis cases, but according to the province's Health Ministry, they're not linked to the main outbreak.

Symptoms of listeriosis can include fever, headache, nausea, vomiting, constipation and diarrhea. Symptoms usually appear within two to 30 days, and up to 90 days after consuming contaminated food.

Since the discovery of the contaminated meat, there's been a massive recall of meat products and sandwiches across Canada.

On Monday, Maple Leaf upgraded a precautionary recall of 23 of its products, issued last week, to all 220 packaged meats from the plant.

The Saskatchewan Health Ministry said it's working to make sure food that may have caused the illness is removed from hospitals, long-term care facilities, personal care homes and daycares.

People who are healthy are a low risk of becoming sick from listeria, the Health Ministry said. However, the bacteria poses a risk to the elderly, the very young, those with weakened immune systems and pregnant women.