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Norovirus and gastrointestinal illness cases in Canada have spiked in recent months, and the Public Health Agency of Canada is now working with provincial officials to investigate the rise.

Gastrointestinal illness cases have been linked to raw oysters from B.C. farms, and those facilities have been shut down. But the health agency explained that it’s not clear what, exactly, caused the problem.

READ MORE: 9 cases of gastro-intestinal illness in Alberta could be linked to raw B.C. oysters

What’s especially concerning is that the number of cases are still rising, which indicates that infected oysters are still being sold at grocery stores or restaurants.

Here’s what Canadians should know about the rise, and the raw oysters associated with the illnesses.

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Rise in Canada

While no deaths have been reported, many individuals reported becoming sick between mid-March to early April after eating B.C. oysters.

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According to the public health agency, there are currently 126 reported cases of gastrointestinal illnesses in the country directly related to oysters — 92 in B.C., nine in Alberta and 25 in Ontario.

Though not all the cases have been tested, the health agency says that norovirus is the dominant infection.

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What exactly is norovirus?

Norovirus is a common gastrointestinal illness in North America that is not known to be deadly, but it does have several uncomfortable symptoms.

The most common are nausea, vomiting, diarrhea and stomach cramps, but others can include a fever, chills and aches. Those with weaker immune systems, such as pregnant women, young children or the elderly, may develop more severe symptoms.

Jason Tetro, a microbiologist and infectious disease expert, told Global News that the symptoms can be very uncomfortable, with uncontrollable vomiting or severe diarrhea.

“You literally turn into an explosion,” Tetro said. Tweet This

The virus typically begins 24 to 48 hours after exposure and generally lasts about two days.

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How does it spread?

The health agency warns that the virus is very contagious.

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People can become infected with it through human contact, things like sharing food or utensils, or changing the diaper of a sick child. It can also be spread through infected surfaces, such as door handles or counter-tops.

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In this outbreak’s case, it was spread through the consumption of contaminated food.

Norovirus can live on surfaces for months, Tetro explained.

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How to safely handle and eat oysters

The health agency warns that oysters should be fully cooked in order to kill norovirus — partially cooking will not solve the problem. That means they should be cooked to an internal temperature of 90 C, or 194 F.

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Oysters that don’t open while cooking should be thrown away, and any leftovers should be refrigerated immediately.

Surfaces that the oysters touch, as well as hands, should be cleaned and properly disinfected.

— With previous Global News files