MAY 11, 2018 7:45 AM PDT

Norovirus Outbreak Linked to Oysters

Norovirus is a gastrointestinal bug that causes nausea, vomiting, and diarrhea. While many know it as the “Cruise Ship” bug because it’s common in contained spaces, it can be problematic in any location. It’s spread by coming in contact with the stool or vomit of an infected person, and recently in Canada, there was an outbreak that was traced to oysters. 

Public health officials in Canada first announced the spate of cases on April 9, 2018. At that point, there were 40 confirmed cases. The number of people infected has risen, however, and now stands at about 126 cases of the illness across three provinces. In British Columbia there were 92 cases, in Alberta, there were 9 and Ontario reported 25 cases. Patients started becoming ill in mid-March, and early April and all who were sickened had consumed oysters from British Columbia.  

Canadian health officials are working with provincial health departments as well as federal agencies. It is known that the norovirus came from the oysters. However, the shellfish could have been contaminated in different ways. Norovirus can be foodborne if an infected person does not clean up after using the bathroom or being ill. Handwashing is critical in norovirus outbreaks since the disease is so easily spread. It’s also possible that the oysters were contaminated before being harvested. It’s possible that if raw sewage were to leak or flow into fishing grounds, the oysters would be exposed to contaminants before ever leaving the water. 

One of the reasons oysters are a common way for norovirus to spread is that many people eat them raw. To kill norovirus, food should be cooked at 90° Celsius or 194° Fahrenheit for a minimum of 90 seconds. Raw food, such as oysters and other seafood like sushi and sashimi, can increase the risk of becoming ill from foodborne pathogens. 

While the oyster farms in British Columbia that produced the tainted oysters have been closed as a precaution, officials say it’s likely that some contaminated oysters remain on the market. While it’s easy to tell when fish or seafood has gone bad or is old, norovirus cannot be detected just by how food appears. An oyster could be teeming with norovirus, but still look, smell and taste completely fine. 

Public health agencies in British Columbia have issued some safe handling tips for oysters, which include cooking them. If you must have them raw, make sure they are kept separately from cooked food to avoid cross-contamination. Use different utensils and plates for cooked food and raw food, and sanitize all cutting boards and surfaces after preparing food. It goes without saying that washing your hands after using the bathroom is the number one way to prevent infecting another person or contaminating food. Norovirus is especially virulent, because it survives on surfaces for up to 24 hours and it can even survive cold temperatures. Some cleaning products do not kill norovirus, and this only adds to the difficulty of isolating an outbreak. Products that contain bleach are being recommended by officials in Canada to curb the spread of the illness.

Norovirus symptoms include diarrhea, vomiting, nausea and abdominal cramps. A low-grade fever can also go along with the virus as well as a headache, muscle aches, and fatigue. Pregnant women, the elderly and those with compromised immune systems are especially at risk. Symptoms can show up as soon as 12 hours after infection, or it could take as long as 48 hours to fall ill. A person who has been exposed can be contagious before symptoms appear, so it’s imperative to be proactive with hygiene. 

Sources: Food Safety News, Public Health Agency of Canada

About the Author
  • I'm a writer living in the Boston area. My interests include cancer research, cardiology and neuroscience. I want to be part of using the Internet and social media to educate professionals and patients in a collaborative environment.
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