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Q&A: Listeria

The Globe's public health reporter answers key questions about listeria

From Tuesday's Globe and Mail

What is Listeria?

Listeria monocytogenes are bacteria that can cause a food-borne illness called listeriosis. The bacteria are common in the environment and have been known to contaminate soft cheeses made from unpasteurized milk, raw meat, unwashed vegetables, deli meats and hot dogs.

Is it dangerous?

Healthy people can fight off many bacterial infections. The symptoms of listeriosis are similar to food poisoning - vomiting, diarrhea, fever. It can be treated with antibiotics. In people with compromised immune systems - the elderly, babies, cancer patients - listeriosis can be dangerous, leading to life-threatening encephalitis and meningitis.

Those at greatest risk are pregnant women because listeriosis can provoke miscarriage and stillbirth, and infect the fetus.

Are all deli meats


The current outbreak has been linked to one plant, the Maple Leaf Foods Inc. plant on Bartor Road in Toronto - also known as facility 97B. Specifically, the contamination seems to have occurred on production lines 8 and 9, although the company has recalled all products made at the plant.

To know whether you have deli meats that are part of the recall, look for the code 97B near the "best before" date on the package. Maple Leaf says it produces 220 products at the Toronto plant.

How safe is deli meat?

Deli meats, cold cuts and the like are cooked, which kills most bacteria and other pathogens. In this case, the listeria contamination almost certainly occurred during packaging, either through the ventilation system or on a worker's clothing.

Because pathogens multiply with time, and listeria thrives in the cold, it is important to respect the "best before" date on the package.

What should I do with the deli meats in my fridge?

"If in doubt, throw it out," says Dr. David Waltner-Toews, author of Food, Sex and Salmonella: Why Our Food Is Making Us Sick. Pregnant women, in particular, should not eat deli meats, nor should the meats be fed to babies, the frail elderly, or anyone with an illness that compromises their immune system.

Where does the meat come from?

Deli meats can be from a single source - say ham - or a concoction of meats such as chicken, beef and pork with the odd olive thrown in for good measure. Because of the risk of contamination, slaughter facilities are always separate from processing plants. Companies like Maple Leaf have a vast array of suppliers but also strict safety standards.

If listeria is common, why has it suddenly

become dangerous?

While the organism is common in the environment, as food-borne illnesses go, listeriosis is fairly unusual. Canada has only about 100 cases each year, and few deaths, so when a couple of fatal cases occur in nursing homes in close proximity, alarms are raised.

Additionally, scientists can now do genetic fingerprinting to identify the strain at the root of the outbreak to distinguish it from isolated cases.

Is the worst

of the outbreak over?

At this point, that's impossible to say. Listeria can

incubate for months. To date, there have been 12 deaths linked to the outbreak and 26 confirmed cases of listeriosis in four provinces. But history tells us that the toll could go much higher.

In 1985, in Los Angeles, 48 people died (most of them babies) after eating unpasteurized cheese contaminated with listeria. In 1981, 48 people in the Canadian Maritimes were sickened by coleslaw contaminated with listeria; a dozen of them died, and they were almost all infants.

To date, there have been no reports of babies dying or of stillbirths associated with the contamination of deli meats, and public health experts see that as unusual.

What does this outbreak tell us about the safety

of our food supply?

It's noteworthy that listeriosis was virtually unknown before the advent of "ready-to-eat" foods. Incidents of food poisoning and contamination used to be fairly contained and local.

Now, given the way food is produced, processed and distributed through vast networks that span continents, outbreaks of food-borne disease can stretch far and wide.

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