A Canadian outbreak of norovirus traced to raw oysters is now on the U.S. radar as federal and state officials report they are investigating a multistate outbreak in this country.
More than 170 people across three Canadian provinces, Alberta, British Columbia and Ontario, had been infected by the highly contagious virus as of the most recent report from the Public Health Agency of Canada. The health agency and the Canadian Food Inspection Agency have been working on the outbreak investigation since early April.
Monday evening the U.S. Food and Drug Administration issued its own outbreak investigation notice. Complete distribution details were not yet available, but the FDA reported with certainty that the Canadian oysters have been sent to California, Illinois, Massachusetts, and Washington.
“It is possible that additional states received these oysters either directly from Canada or through further distribution within the U.S.,” according to FDA’s notice.
“FDA and the states are conducting a trace-forward investigation to determine where the raw oysters were distributed and ensure they’re removed from the food supply. Retailers should not serve raw oysters harvested from the following harvest locations (or landfiles) within Baynes Sound: #1402060, #1411206, #1400483, and #278757.”
Although the FDA outbreak notice reported the agency is working on the outbreak investigation with the U.S. Centers for Disease Control and Prevention, the CDC had not posted any information about the situation as of 10 p.m. Monday. The FDA did not report how many people have been sickened in the outbreak in the United States.
In Canada, people became sick between mid-Arch and mid-April, according to public health officials. The Public Health Agency of Canada reported on April 27 that the number of new cases was beginning to taper off. Federal officials in Canada have closed the implicated shellfish until further notice.
“Most individuals who became sick reported eating raw oysters from the south and central parts of Baynes Sound, British Columbia, before the onset of their illness,” the Canadian agency reported. The investigation into a specific source of contamination impacting the shellfish farms in that area is ongoing.
“Although not all cases of illness have been tested, testing of several cases has confirmed the presence of a norovirus infection. It is suspected that norovirus illness caused by the consumption of contaminated oysters is the cause of illness in the untested cases.”
Advice to consumers
Raw oysters can cause illness in anyone, but they are particularly dangerous for young children, older adults, pregnant women and people with compromised immune systems. Oysters and other food contaminated with noroviruses usually looks, smells and tastes normal.
Many foodborne pathogens can be found in raw oysters, including bacteria, parasites, and life-threatening viruses. Some foodborne illnesses caused by oysters, such as listeriosis, can take up to 70 days after exposure for symptoms to develop. Norovirus, however, usually causes symptoms within 12 to 48 hours after consuming contaminated foods or beverages.
Most people infected with norovirus develop diarrhea, vomiting, nausea and stomach pain. Diarrhea tends to be watery and non-bloody. Diarrhea is more common in adults and vomiting is more common in children. Regardless, symptoms can easily result in dehydration requiring intravenous fluids.
People who think they might have become ill from eating possibly contaminated oysters should talk to their healthcare providers. Contact your healthcare provider if you have diarrhea that lasts for more than three days, or is accompanied by high fever, blood in the stool, or so much vomiting that you cannot keep liquids down and you pass very little urine.
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