Raw oysters, so good with hot sauce, are being blamed more and more for making people really sick.
And I mean a lot of people.
The U.S. Centers for Disease Control and Prevention in Atlanta is tracking an increase in infections from Vibrio, a saltwater-based bacteria that is found in shellfish, and in this case, oysters. The CDC says 13 states are reporting the increase. Vibrio infections spiked 75% last year to the highest levels seen since 1996, when tracking of the bacteria’s effects began. That translates to roughly 80,000 people.
What is most concerning is that the West Coast version of the bacteria is now being found in oysters on the East Coast. Nobody knows why. And what’s also curious is while Vibrio is not usually associated with shellfish farms, it is being found there as well.
The thing is, we know how to control Vibrio. It is a bacterium that is found in seawater. But because oysters are filter feeders, Vibrio builds up to dangerous levels in the shellfish.
However if you cook the oyster, or freeze it, the Vibrio bacteria die. The CDC says “Vibrio infections can be prevented by postharvest treatment of oysters with heat, freezing, or high pressure, by thorough cooking, or by not eating oysters during warmer months.” In other words, if you don’t eat a raw oyster, you are safe.
The definition of cooking shellfish means an internal temperature of 145 degrees for 15 seconds. If you are steaming oysters, a good rule of thumb is to steam the oyster until it pops open, then continue steaming for 3-5 minutes afterwards to ensure the Vibrio bacteria are killed.
Here are more oyster eating tips, thanks to North Carolina Sea Grant.
|What to Look For:||What to Avoid:|
|Plump, cream-colored meat||Shriveled, dark, dry meat|
|Free of shell bits and sand||Presence of shell or sand|
|Clear or slightly opaque liquid, but less than 10% of volume||Cloudy liquid|
|Mild scent||Strong sour or “fishy” odor|
UPDATE (Posted Aug. 4, 2014)
Thanks to everyone who has read my blog on oyster-eating safety tips and commented on it. There are a couple points that may have caused some confusion that I want to make clear.
Vibrio, the bacteria found in oysters, occurs naturally in the water. It is concentrated in oysters because the shellfish are filter feeders. That means Vibrio can be acquired from seawater through open wounds and not just by eating oysters. That also means Vibrio can be acquired through other shellfish such as crabs or clams.
It should also be mentioned that the risk of serious illness from Vibrio is heightened in individuals with pre-existing conditions, such as liver disease, diabetes, or cancer. While anyone can get sick from eating raw oysters with high concentrations of Vibrio, folks with pre-existing conditions are most at risk.
While the CDC says Vibrio accounts for roughly 80,000 illnesses in the U.S. annually, the rate of Vibrio illnesses remains much lower than that of foodborne infections, such as salmonella and campylobacter, which account for 1.2 million illnesses.
While there is a risk to eating raw seafood, many of the cases of Vibrio can be traced to a breakdown in the handling of the shellfish, in which a constant temperature was not maintained. Be sure to check if the shellfish you are going to prepare was handled using established protocols.
Again, thanks for reading!
- Frank Graff
Frank Graff is a producer/reporter with UNC-TV, focusing on North Carolina Science Now, a weekly science series that airs Wednesdays, beginning in August 2013, as part of North Carolina Now on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!