By Lindsay Bosslet
Public Health – Seattle & King County
As waters warm up, shellfish beds become breeding grounds for bacteria, including Vibrio parahaemolyticus or “Vibrio,” one of the most common causes of illness related to raw oyster consumption.
And this year, we’re setting records. Why are so many people getting sick?
We sat down with Vance Kawakami, our communicable disease epidemiologist, to better understand the risk of eating raw and under-cooked oysters.
Vance, is there any safe way to eat raw oysters? Will Tabasco sauce or vodka kill the bacteria? Please say yes.
No, there is no safe way to eat raw oysters, and no amount of alcohol, hot sauce or other condiment will kill the bacteria. The only way to avoid getting a Vibrio infection is to make sure the oysters are thoroughly cooked to an internal temperature of at least 145 degrees Fahrenheit for 15 seconds.
I only eat oysters at King County’s finest restaurants. They’re probably safer than other oysters, right?
Wrong. Even the fanciest restaurants can’t eliminate Vibrio from their shellfish suppliers’ shellfish beds, and they probably won’t know if their latest batch is extra risky until it’s too late.
Of course, restaurants still have a role in reducing risk by keeping raw shellfish at the proper temperature, preventing cross-contamination, and reporting illness when it happens.
Okay, maybe I’ll just start harvesting them myself. Then I can pay close attention to the beds and only harvest disease-free oysters.
Oysters that contain Vibrio don’t look, smell, or even taste different from oysters without Vibrio. With the exception of closed beach signage, you will have no way of knowing if oysters are free of bacteria. If you want to harvest your own oysters I suggest:
- Checking for beach closures and advisories or call 1-800-562-5632 before you plan to harvest
- Harvesting as soon as possible after the tide goes out
- Don’t harvest oysters that have been exposed to direct sunlight for more than two hours
- Refrigerating or icing oysters immediately after harvesting (keep at less than 41 degrees Fahrenheit)
I eat raw oysters all the time, and I haven’t gotten sick. Maybe I’m immune?
Sorry! Anyone eating raw or under-cooked shellfish should consider themselves at risk for infections from Vibrio. Certain health conditions put people at greater risk of illness. People with weakened immune systems and chronic liver disease are at greater risk of becoming ill, but even otherwise healthy persons who take antacids might also be at greater risk of getting sick and should avoid raw and under-cooked oysters.
What’s up with that? Why are we hearing about so many people becoming sick with Vibrio after eating raw and under-cooked oysters this year?
We don’t know for sure. Vibrio growth is favored by warmer water temperatures. Salinity, water depth, and post-harvest handling may also influence Vibrio levels. Studies are underway that we hope will help us better understand Vibrio and prevent illness. In addition, it is likely that greater public awareness of Vibrio associated with raw and under-cooked shellfish and recent increases in the use of more sensitive diagnostic tests to diagnose Vibrio are contributing to the increase in reports. What we do know is that eating raw and under-cooked oysters is risky business anytime of the year.