Maple Leaf Foods upgraded a recall of 23 of its products to all 220 packaged meats processed in a Toronto plant. (CBC)

While consumer anxiety is increasing with news that 15 Canadians have died in a listeriosis outbreak, a Calgary professor says the recall of deli meats connected with the cases likely won't affect people's buying habits in the long run.

On Monday, Maple Leaf Foods upgraded a recall of 23 of its products to all 220 packaged meats processed in a Toronto plant after tests confirmed it was linked to the outbreak caused by the bacterium Listeria monocytogenes.

Since then, several other companies, including Calgary-based Lucerne Foods which supplies Safeway and Mac's stores in Alberta and Saskatchewan, have pulled their ready-made sandwiches that contained some Maple Leaf meat products from store shelves.

Public health officials confirmed 29 cases of listeriosis on Tuesday, including 15 deaths. Of an additional 30 suspected cases, four are in Alberta, said the Canadian Food Inspection Agency.

Symptoms of listeriosis — which include high fever, severe headache, neck stiffness and nausea — occur up to 70 days after consuming contaminated food.

Calgary-based Lucerne Foods has recalled ready-made sandwiches that contained some Maple Leaf meat products from store shelves. (CBC)

Some shoppers in the parking lot of one Calgary grocery store said they never buy processed meats, but others who do said they've stopped.

"I would not probably buy any of that product for at least six months," one woman told CBC News, citing the "fear factor."

But Debi Andrus, a marketing professor at the University of Calgary, said the boycott is a knee-jerk reaction that will ease in six to nine months, which is the average "stay away" time.

"Because of the type of product it is, it won't be for good," said Andrus. "But people are going to be more cautious and want to look at the labels, and see where it's made."

Andrus said people like to make sure they understand what happened, and that they've been reassured the problem's fixed.

Business booming at natural food stores

"It'll start with the supply chain," she said. "People will start buying again from Safeway or Lucerne, and then certainly they'll start buying from the chains, like Mac's and that, and then Maple Leaf will be the last one, where we'll see people starting to buy them but limited.

"Consumers really have to feel that the problem has been discovered, and the solutions have been found."

The recall has meant new business for natural food stores.

Patty Nowlin, the owner of Community Natural Foods in Calgary, said she's been seeing more customers interested in where their food is coming from — which she says is common after a food recall.

"[They're] asking more questions, which is really great because we're able to educate them, and it sustains itself, it's not like a one-week or a one-shot deal. They are coming back and becoming interested in the topic," she said.

The Sunnyside Market, another natural food store, also reported a spike in business.