Researchers with the BC Centre for Disease Control may have pinpointed how a mysterious norovirus outbreak spread, forcing the closure of 13 West Coast oyster farms and curtailing operations at others as hundreds of Canadians fell ill.
An article published in the latest edition of the British Columbia Medical Journal says sewage is often the cause of ocean contamination and contaminants spread by currents affected oyster farms on the east and west coasts of Vancouver Island.
Researchers determined the norovirus outbreak began last November and made more than 400 people sick across Canada by March, but investigators were initially uncertain how a single source of the illness could affect such a huge area.
The article says it’s still unclear if one or many sewage sources were involved, but a wet fall and unseasonably cold winter could have enhanced norovirus survival and allowed oysters to retain tainted ocean sediments longer than usual.
The authors also say the outbreak disproves claims that shellfish is safe to eat between September and April â€” months containing an ‘r’ â€” noting that bacteria and viruses persist in cold seawater and marine biotoxins occur year-round.
Darlene Winterburn, executive director of B.C.’s Shellfish Growers Association, says the Public Health Authority of Canada declared the outbreak over in early May and all but one of the affected farms has reopened.
She says the article may offer answers to the recent outbreak, but an exact cause may never be identified and the industry continues to work with the Centre for Disease Control, Canadian Food Inspection Agency and the departments of Fisheries and Environment.
“The theories are very diverse and at this stage of the game, the unfortunate reality is that it is going to be very difficult to prove any because we don’t have (norovirus) in the water right now.”
She says the industry wants to learn from the outbreak and make changes to ensure it responds better, if it happens again.