The public health department of Niagara's regional government said Tuesday that tests have confirmed that a second Niagara senior, a Niagara Falls man who died this month, had eaten food contaminated with the bacteria Listeria.

Public Health said tests revealed last week that another senior, a St. Catharines woman who died in June, was the first confirmed Listeria-related death in Niagara.

Maple Leaf Foods has initiated a massive recall of more than 200 meat products produced at a processing plant it operates in Toronto.

The Public Health Agency of Canada said Tuesday that the number of confirmed Listeria cases has now ballooned to 29 in four provinces, and that 12 deaths -- including 11 deaths in Ontario -- have resulted. A further 29 cases are under investigation, the agency said.

Dr. Doug Sider, associate medical officer of health for the region, said it's probably impossible to say Listeria was directly responsible for the St. Catharines senior dying, since older people are more likely to have co-existing, chronic physical problems.

Often, it's a combination of factors that lead to death, he said.

Test results from a federal lab in Winnipeg last week did indeed show, though, that the St. Catharines senior tested positive for the strain of Listeria at the centre of the outbreak, Sider said.

Niagara residents, meanwhile, are being told to rummage through their fridges and freezers to look for any of the more than 200 Maple Leaf Foods products that have been recalled. Recalled meat products likely have the numbers 97B on the packaging.

The Public Health Agency of Canada said if for any reason you do not know where your ready-to-eat meats came from, play it safe and throw the food out.

Federal Health Minister Tony Clement said Sunday night that more Listeria cases are expected because of the often long incubation time before people who consume food contaminated with Listeria show symptoms.

Those symptoms, which include flu-like symptoms such as nausea, vomiting, cramps, diarrhea, headache, constipation and persistent fever, usually surface within two to 30 days of eating contaminated food. But in some cases it can take as long as 70 days to show up, the Canadian Food Inspection Agency says.

Health Canada says few people who eat food contaminated with Listeria will actually develop serious symptoms, known as listeriosis. Those most likely to become ill are pregnant women, the elderly and people with weakened immune systems, such as people with AIDS, people with diabetes and those undergoing chemotherapy.

"It's a rare infection," said Sider. "Most people don't get ill."

Flu-like symptoms can develop into potentially fatal brain infections or blood poisoning. Health Canada says 20 to 30 per cent of foodborne listeriosis infections in high-risk people can be fatal.

There is no vaccine to prevent listeriosis.

The Canadian Food Inspection Agency has a full list of recalled food products listed on its website at www.inspection.gc.ca.

The region also have a Listeria link on its website at www.regional.niagara.on.ca.