While only 5 percent of all food borne illnesses are seafood related, 85 percent of those illnesses can be traced to eating raw mollusks such as clams, oysters and mussels. Naturally occurring bacteria that thrive in a salty environment, marine toxins related to algae blooms and polluted runoff-related viruses and bacteria that enter harvest areas can all be responsible for illness.
There are shellfish that are at risk of cross-contamination that are also eaten raw, such as abalone and lobster, and those mollusks of which only muscle is eaten, like scallops and goeduck clams.
Local, state and federal health agencies regularly monitor shellfish beds and farms. Water and shellfish samples are taken from the harvest areas weekly and are analyzed for the presence of natural toxins and pathogens, and harvest areas are closed if anything is detected. Harvest areas are also shut down as a precaution during heavy rains.
In brief, where your raw shellfish comes from and how it is handled is key in assuring safety.
To avoid consuming contaminated raw shellfish:
• Purchase seafood from a clean shop with knowledgeable employees and displays National Shellfish Sanitation Program (NSSP) tags with all mollusks. The NSSP requires mandatory tracking of harvest location and dating of all commercially harvested shellfish to ensure that the harvest has taken place in waters that are certified to be safe at the time of harvest.
(The harvest of contaminated shellfish by ill-informed recreational harvesters is responsible for the great majority of shellfish-related illness.)
• Give first preference to locally grown shellfish without far to travel.
• Eat raw shellfish only in clean restaurants where you have confidence in the abilities of the chef and staff.
• Eat raw shellfish during the cool winter months. Warmer waters encourage algal blooms and in some locations, refrigeration can be compromised.
• Avoid raw shellfish in areas of the world where sanitary systems may be inadequate, especially in the warmer areas of the tropics.
To be safe, pregnant women, young children, individuals with diabetes, cirrhosis, leukemia, AIDS, or chronic disease, such as those with immunosuppressive drugs or chemotherapy should not consume raw shellfish at any time.