Raw and undercooked B.C. oysters have now been linked to 289 cases of gastrointestinal illnesses in three different provinces.
As of March 6, there were a total of 201 cases in British Columbia, 40 in Alberta and 48 in Ontario.
No deaths have been reported.
Individuals became sick between December and February, and all of those who became ill reported having eaten oysters.
As a result, four shellfish farms, where oysters are harvested in British Columbia, have been shut down. Investigations into other harvest areas that have been linked to illnesses are ongoing as gastrointestinal illness linked to consumption of oysters continues to occur.
The Public Health Agency of Canada says it is working with federal and provincial public health partners to investigate what’s causing people to get sick.
It says even though the source of illness has been identified as B.C. oysters, the cause of the contamination has not been identified.
The outbreak is ongoing, which indicates contaminated oysters remain on the market — including at restaurants, seafood markets and grocery stores.
That means there is still a risk of norovirus infection and gastrointestinal illness associated with the consumption of these oysters.
Although not all cases of illness have been tested, testing of several cases has confirmed the presence of norovirus infection. It is suspected that norovirus illness, caused by the consumption of contaminated oysters, is the cause of illness in the untested cases.
Noroviruses are a group of viruses that can cause gastroenteritis in people, an illness that usually includes diarrhea and/or vomiting and are found in the stool or vomit of infected people.
They are very contagious and can spread easily from person to person.
People with norovirus illness usually develop symptoms of gastroenteritis within 24 to 48 hours, but symptoms can start as early as 12 hours after exposure. The illness often begins suddenly. Symptoms include diarrhea, vomiting, nausea and stomach cramps, low-grade fever, headache, chills, muscle aches and fatigue.
But some foods can be contaminated at their source. For example, shellfish like oysters, may be contaminated by sewage in water before they are harvested.
However, food contaminated with noroviruses may look, smell and taste normal.
Acute gastrointestinal illnesses such as norovirus illness are common in North America and are very contagious, affecting all age groups. However, pregnant women, people with compromised immune systems, young children and the elderly are at risk for developing more serious complications, like dehydration.
How to protect yourself
The illness can be avoided if oysters are cooked to an internal temperature of 90 C for a minimum of 90 seconds, and proper hand washing and food safety practices are followed. Lightly cooking oysters does not kill norovirus.
Discard any oysters that do not open when cooked, eat oysters right away after cooking, refrigerate leftovers and always keep raw and cooked oysters separate.
Wash your hands well with soap before handling any food and be sure to wash your hands, cutting boards, counters, knives and other utensils after preparing raw foods.
Noroviruses can survive relatively high levels of chlorine and varying temperatures. Cleaning and disinfecting practices are the key to preventing further illnesses in your home.