After a year of being perplexed by a massive norovirus outbreak linked to B.C. oysters, local scientists have one theory about why so many people got sick.
In a paper published in the July issue of the BC Medical Journal, researchers from the BC Centre for Disease Control postulate that this year's wet and cold winter enhanced the survival of norovirus in municipal sewage that was carried to oyster farms via ocean currents.
Between November 2016 and March 2017, more than 400 people across Canada got sick with the gastro-intestinal virus from eating B.C. oysters.
Norovirus is highly infectious, and is typically spread from person to person. Foodborne outbreaks of norovirus are often linked to sick food handlers. But this case was different— oysters were contaminated while still in their marine environment, and the infected oysters came from spread out oyster farms on both coasts of Vancouver Island.
That's why sewage spread by ocean currents seemed like the most likely culprit for these scientists.
Once oysters were contaminated by sewage, the unseasonably cold winter last year enabled the virus to survive until the oysters were consumed by people.
"Wet, cold and dark winters enhance norovirus survival, allowing for longer retention in ocean sediments and in oysters," the article reads.
The scientists are investigating sewer overflows, metropolitan treatment plants, municipal raw sewage discharge and commercial fishing vessels as possible sources of the oyster contamination.
They also wanted to dispel the common myth that it's safe to eat shellfish in months that end with an "r"—September to April. In fact, both bacteria and viruses can persist in cold seawater.
