Vibrio parahaemolyticus in raw/undercooked shellfish

Two cases of diarrheal illness due to the bacteria Vibrio parahaemolyticus (vibriosis) have been reported in Idaho in the last three months, compared with a total of two cases during 2005 through June 2011. Both ill persons consumed raw oysters from domestic coastal sources.

Vibriosis is an intestinal disease caused by bacteria in the genus Vibrio. Vibrio are found naturally in marine coastal waters, normally in low numbers that pose no problems.  Vibrio multiply rapid in warm conditions, so fish and shellfish are more likely to be contaminated in the summer.  The commercial shellfish industry follows strict refrigeration and handling requirements during warm summer months. Failure to keep shellfish cold after harvesting can contribute to the growth of the bacteria. Most cases of vibriosis from Vibrio parahaemolyticus occur from eating raw or undercooked shellfish, particularly oysters. Poor food handling practices during preparation can also lead to illness. Fully cooked food can be contaminated if rinsed with seawater.

Anyone can get vibriosis. People taking antacids are more likely to get sick because the stomach acid helps kill bacteria. Symptoms include diarrhea, abdominal cramps, nausea, vomiting, headache, fever, and chills.  Symptoms usually appear about 15 hours after consumption but can take as long as four days to appear.

The illness is usually mild or moderate and runs its course in 2-3 days.  Treatment is not necessary in most cases. Ill persons should drink plenty of liquids to replace fluids lost through diarrhea. Severe cases might require use of antibiotics and hospitalization. If you have persistent severe diarrhea or fever and you think you might have vibriosis, contact your primary care provider.

To prevent vibriosis, eat only well-cooked shellfish, especially in summer months. Do not consider shellfish to be fully cooked when the shells just open – they need to cook longer and reach 145° F for 15 seconds.

×          For oysters in the shell, FDA suggests boiling for 3 to 5 minutes after the oysters open, or steaming by adding oysters to water that is already steaming and cook for 4 to 9 minutes after they open. Discard any oysters that do not open during cooking.

×          For shucked oysters, FDA recommends boiling or simmering for at least 3 minutes or until the edges curl, or frying at 375 ° F for a least 3 minutes, or broiling 3” from heat for 3 minutes, or baking at 450° F for 10 minutes.

Never allow raw seafood or seawater to come in contact with cooked food. Never leave seafood out of the refrigerator for more than 1 hour when temperatures are above 90° F.

CDC information, http://www.cdc.gov/nczved/divisions/dfbmd/diseases/vibriop/.

FDA information, http://www.fda.gov/Food/ResourcesForYou/HealthEducators/ucm085368.htm

Recreational Shellfish Harvesting: Safe handling, storing, and cooking practices.