Tips for enjoying safe shellfish in summer

By Dr. Bob Rheault

musselsThe July 19th Providence Journal published a Health Department advisory stating that shellfish consumers should cook all shellfish.  With proper handling most shellfish are safe to consume raw, but everyone needs to learn how important it is to keep shellfish cold during the hot summer months to avoid illness.  The illness that prompted the advisory was the result of Vibrio parahemolyticus bacteria (V.p.) that came from recreationally-harvested shellfish.  Here are some important facts that all shellfish lovers should know.

Vibrio bacteria are common in all marine waters, usually occurring in moderate numbers with greater abundance in warmer waters.   Levels in shellfish are typically safe unless your shellfish are steaming in a shallow tide pool or exposed on a tidal flat.  It takes a significant dose to cause illness. Scientists believe that for V.p. that dose is about 30,000 cells.

Shellfish concentrate bacteria while they feed and once they clam up, the bacteria inside start to multiply.  A safe dose can become a dangerous dose if shellfish are not chilled within a few hours.  Vibrio growth rates are determined by temperature. At 90 degrees F the bacterial population will double every hour, at 60 degrees growth slows dramatically, and below 50 degrees the growth of V.p. stops altogether.

It is rare, but possible, for shellfish right out of warm waters to have enough Vibrios to cause illness.  It is far more likely that safe shellfish were made unsafe because they were not chilled before a few doublings occurred.  If you can get your shellfish down to 60 degrees as soon as possible, and down to 50 within 5 hours – your risk of illness should be negligible.  However, if you leave your shellfish in the sun or the trunk of your car for a few hours, all bets are off.  Put shellfish in a cooler with an ice pack as soon as possible. If you use ice do not let them sit in the meltwater. Likewise, if you are buying shellfish, don’t let them warm up while you do your errands.

Commercial harvesters and shellfish farmers are strictly regulated and we know how important it is to keep our shellfish shaded and cool.  In summer many of us bring ice out with us and get our product into the dealer’s cooler within a few hours of harvest.  Immuno-compromised individuals should always cook their shellfish and not eat ANY undercooked proteins; no raw shellfish, no undercooked shrimp, no rare hamburger.  If you are unsure if you are immuno-compromised, ask your doctor.

For more information about Vibrios and delicious recipes visit our website

Dr. Bob Rheault is an adjunct faculty member at the University of Rhode Island and is the Executive Director of the East Coast Shellfish Growers Association