You may have heard about recent cases of foodborne illness and oysters. According to the Food Safety News (3/22/2023) 170 cases of illness were reported, in Europe and Hong Kong, from eating raw oysters. Samples from oyster batches in the Netherlands, France, and Ireland, as well as from restaurants and ill people, have tested positive for Norovirus.

The United States Food and Drug Administration has issued another advisory against eating oysters harvested in British Columbia between January 16 and February 17 of this year (see the recall notice FDA Advises Restaurants, Retailers and Consumers to Avoid Raw Oysters from Deep Bay, British Columbia, Canada Potentially Contaminated with Norovirus) This was also an illness involving norovirus. (Note: you and/or your food supplier should subscribe to the FDA’s recall notice list as well as the certified shellfish shippers list.)

This report might be a surprise to many. Certified food managers learn that oysters are most often associated with contamination from vibrio vulnificus. However, oysters are filter feeders, gathering nutrients from waters in their harvest areas. Contamination in these waters might be caused by sewage containing both bacteria and viruses (this is a good reason to subscribe to any information about unapproved shellfish sources). While vibrio vulnificus is a bacterium, both Norwalk and Hepatitis A are viruses and could be present in sewage contamination. (Be aware, however, that some bacteria like vibrio vulnificus thrive in otherwise uncontaminated waters!)  Food safety consultation and regulations require holding shellfish certification tags for at least ninety (90) days past the last date of sale, in consideration of the lengthy incubation (the time from when food is consumed to the start of symptoms) time for the virus hepatitis A.

What will not be surprising is the age groups affected by these illness cases, individuals above 65 and below 5 years old. (In the case of all three potential shellfish contaminants (vibrio vulnificus, norovirus and hepatitis A virus) a small amount of contamination can cause illness.

While clear precautions are to purchase shellfish from approved suppliers and retain the certification tags for each shipment as required, it’s also important to remember the risk of cross contamination from improper handling. Ill employees should not be allowed to work (be sure all employees have been advised of the need to report illness), and utensils and equipment must be cleaned and sanitized in between uses. The FDA has the following advice:

  • Wash hands with warm water and soap following the cleaning and sanitation process.
  • Exclude food handlers from the operation who are vomiting or have diarrhea and have been diagnosed with Norovirus. Be sure to report this illness to your health authority.
  • Avoid bare hand contact with ready to eat food.
  • Purchase only from reputable suppliers.
  • Retailers, restaurants, and other food service operators who have processed and packaged any potentially contaminated products need to be concerned about cross-contamination of cutting surfaces and utensils through contact with the potentially contaminated products.
  • Retailers that have sold bulk product should clean and sanitize the containers used to hold the product.
  • Regular frequent cleaning and sanitizing of food contact surfaces and utensils used in food preparation may help to minimize the likelihood of cross-contamination.

The FDA also has some interesting information about shellfish, this time oriented to a discussion of vibrio vulnificus. A few of the myths are as follows: purchasing shellfish in colder months will make them safer (actually, 40% of foodborne illness cases from shellfish occur in colder months between September and April); hot sauce kills bacteria (only thorough cooking to approved temperatures – 145 degrees F. for 15 seconds will do that, check your local requirements in case cooking temperatures differ); the old chestnut that states you can smell or taste contamination (all pathogens are odorless and tasteless). See the whole article at › food › health-educators › raw-…