Norovirus removal from shellfish products



We have confirmed strategies to improve the commercial purification and removal/reduction of norovirus (NoV)– the leading cause of shellfish-related gastrointestinal illnesses – from bivalves.
Currently, there is a perception that depuration is largely ineffective in removing NoV from shellfish. The European Food Safety Authority (2012) reported that the most effective method to control NoV infection from oyster consumption was to produce oysters from areas which are not faecally contaminated. Whilst this remains the best means of assuring NoV-free shellfish, our trials have shown that depuration can be effective for certain strains of NoV. 
The method proposed can be used by shellfish producers to ensure their produce is safer, reducing risks to human health.


Result description Norovirus is the principal agent of bivalve shellfish–associated gastroenteric illness worldwide. The main option under European legislation for controlling the risks associated with shellfish originating from class B areas (i.e. generally moderately polluted) is for them to undergo purification (depuration) in tanks of clean seawater to purge themselves of sewage contaminants. Whilst bacteria (e.g. E.coli) are rapidly and effectively removed during this process, norovirus (NoV) is generally not, particularly at the typical temperatures prevailing in the winter at depuration centres in the UK. This study further investigates strategies of commercial purification to assess improvements on the removal of NoV from bivalves as recommended by EFSA (2012).

Our trials considered the effects of temperature, algal feeding (natural algae and commercial preparation), salinity, disturbance and light/dark on NoV removal. Of these different factors, we found that raised temperature (18 °C in our case) had the most significantly improved effect. We found approximately 46 % removal of NoV genogroup II (GII) at 18 °C after two days and 60 % after five days, compared with a maximum of 16 % NoV genogroup I (GI) removal. Twice the rate of NoV GII removal was achieved at 18 °C compared with 8 °C after five days. We found no difference in shelf-life between oysters from trials run at 8 and 18 °C for oysters held at <8 °C for up to 12 days post-depuration. Aside from the salinity trial results (which suggested that this needs to be matched to the salinity the shellfish may have experienced in the natural environment), the other factors trialled, including feeding, had no significant improved effect on NoV removal. 

We have confirmed a method (elevated temperature during depuration) to lower NoV levels from contaminated class B oysters harvested from areas experiencing a temperature climate similar to the UK. Our method reduces health risks by improving seafood safety. Seafood producers and processors can use the method with benefits for consumers worldwide.

Result Type Scientific or Technological R&D Result
Result owner CEFAS
Target audiences Other Actors who can help us fulfill our market potential

International Organisations (ex. OECD, FAO, UN, etc)

Our needs We want to share our results with those working in the shellfish industry and to make regulatory officers (food safety and environmental) monitors aware of our results.
Page updated: 29th October 2019