With a number of cases of life-threatening illnesses caused by a water-borne bacteria being reported recently in the Southeast, people throughout the Gulf states have been wondering if it’s safe to go in the water and eat the raw oysters that come from it.
Vibrio vulnificus and Vibrio parahaemolyticus, both commonly referred to as simply “vibrio,” are bacteria (often mistakenly referred to as “flesh-eating bacteria”) that can enter the body in two ways: through an open wound that is exposed to warm seawater and through ingesting raw oysters.
Working in the favor of scientists and health officials is the fact that the vibrio bacteria are not new. Vibrio has been around, as University of Florida seafood specialist Dr. Steve Otwell points out, “since the Greeks first harvested oysters.” New strategies have been employed to counteract the bacteria since it became a growing health concern in the 70s and 80s.
While the answer over the safety of these two common activities isn’t a simple one, it is a positive one.
Regarding consumption of raw oysters, in the case of Vibrio vulnificus, the red flag isn’t the safety level of the product itself—it’s the health level of the consumer.
“It’s not the water or the oysters that really is the problem so much as the consumer,” said Dr. Otwell. “If the consumer is immune compromised, then the severity is much worse. It’s something we all need to be aware of and try to continue to resolve. But it’s amazing the millions and millions of servings that people do not get ill.”
Anyone currently diagnosed with and being treated for liver disease, cancer, hepatitis, later stages of diabetes, or any other condition that compromises the immune system is strongly advised not to eat raw oysters. Because Vibrio vulnificus enters and infects the blood stream, a weakened immune system may not be able to fight off the infection, which could ultimately prove to be fatal.
Ken Moore, executive director of the Interstate Shellfish Sanitation Conference (ISSC), echoed this sentiment. “People with compromised immune systems are the ones at the greatest risk,” said Moore. “And the degree to which your system is compromised normally dictates the outcome of the illness.”
Highest Safety Standards
While there has always been some level of risk involved in ingesting raw oysters, cases of vibrio derived from oysters in Gulf states have been trending downward in recent years due to the highest possible safety standards among processors and the tremendous steps taken toward pinpointing the safest possible methods of harvesting and handling.
One strategy to enhance the safety of the product, especially for those consumers who are at risk, is referred to as post-harvest processing, or PHP. The most commonly available product form produced by this strategy is an individually quick-frozen (IFQ) oyster with its top shell removed.
Other PHP methods include using high pressure, low-heat pasteurization, and most recently, low-dose irradiation. Another step taken at harvest involves rapid refrigeration of the oysters after harvest.
Newer safety procedures are also currently being discussed. According to Moore, the ISSC will be holding an annual meeting in Salt Lake City in late October to discuss different strategies and control options.
Education and Awareness
But perhaps the most important method of promoting safe oyster consumption is the simplest one: education.
“There has been a huge educational campaign for decades now,” said Dr. Otwell. “Right now, there is a model ordinance for the harvest of shellfish in the United States that recommends that all servings of raw product should be coming with advisory statements, and in certain states it’s the law.”
Consumer education also extends to an equally common method of contracting the vibrio bacteria: exposing an open wound to seawater. This sort of infection, which was commonly referred to as “seafood poisoning” or “shrimp poisoning” before vibrio was diagnosed, can range in severity but can ultimately prove to be just as fatal.
Know the Difference
Regarding oyster consumption, it’s worth noting that there is a difference between Vibrio vulnificus and Vibrio parahaemolyticus. The latter is a less-severe strain of the vibrio bacteria that most commonly causes gastroenteritis but can also be fatal in customers with compromised immune systems.
Additionally, according to Moore, Vibrio parahaemolyticus is controlled in the Gulf better than any other coastal region in the U.S.
“We think we have controlled Vibrio parahaemolyticus in the Gulf quite well,” said Moore. “The number of cases that we’ve seen in the Gulf hasn’t really increased. We don’t find the level of illnesses that we see in the Gulf to be unacceptable. We think that the control strategies that we have are about as effective as we can expect given the nature of the food that’s being consumed.”
Enjoy the Oyster
Regarding both common strains of vibrio, the biggest message to take away is that, while there has always been a risk, healthy consumers should not be afraid of eating raw oysters.
For those seafood lovers who have an underlying condition making them susceptible to vibrio, or for those who are unsure of their risk, oysters aren’t off the menu—just remember to eat them cooked, and consult your doctor to make sure cooked oysters are an acceptable part of your diet.
“The oysters of the United States are extremely safe,” said Dr. Otwell. “They’re harvested from approved waters, we have the most stringent safety regulations of any food in North America, and the safety regulations for oysters in the U.S. are more stringent than most countries of the world. That’s why our products are preferred throughout the world.”
For more information about oyster safety, visit the U.S. Department of Health and Human Services, the Interstate Shellfish Sanitation Conference, and Be Oyster Aware.