By: Kate Delany
Raw oysters are a definite foodie trend, with some gourmet food trucks now even offering this menu item. However, eating raw oysters comes with some serious food safety risks. Scientists and food safety experts are at work to inform the public about the risks associated with raw oysters and to potentially ameliorate these risks using new eco-friendly options.
As the CDC notes, “Because oysters feed by filtering water, bacteria can concentrate in their tissues.” The particular bacteria of concern for those who eat raw oysters is Vibrio. Different strains of Vibrio have been detected in raw oysters. All have the capacity to cause human illness though they differ in potency and risk.
Just last year alone, we talked about how climate change is making the prevalence of Vibrio more commonplace.
Illness in Humans from Oysters
Human infection caused by Vibrio is called vibriosis. There are about a dozen type of Vibrio that can cause vibriosis but most infections are caused by just two. The most common culprits are V. parahaemolyticus and V. vulnificus.
Both of these bacteria naturally occur in warm coastal areas. The bacteria is more concentrated during the warm summer months when the warmer water temperatures allow the bacteria to thrive. As the CDC states: “About 80% of infections occur between May and October when water temperatures are warmer.” This does not mean, however, that infection cannot occur in cooler months.
When a person ingests a raw oyster with Vibrio in its tissue, the bacteria enters the human digestive system where it multiplies quickly. The symptoms of V. parahaemolyticus usually manifest themselves shortly after contact. As noted on Foodsafety.gov, the incubation period is typically 2-48 hours.
When an otherwise healthy person contracts this strain of the illness, the primary symptoms are vomiting and diarrhea with attendant abdominal pain. An individual with health concerns (such as cancer, diabetes, immune deficiency, etc.) may also experience fever, chills or potentially even go into shock.
V. vulnificus can cause much more severe symptoms and complications. It may take up to a week for infection with this strain of the Vibrio bacteria to become manifest. In addition to vomiting, fever and diarrhea common to all vibriosis, those infected with V. vulnificus may develop blistering skin lesions. Bloodstream infections are also possible. V. vulnificus infection requires the use of antibiotics, often in an intensive care setting. Limb amputation may be necessary to remove infected tissue.
Vibrio bacteria cause about 80,000 illnesses and 100 deaths each year in the United States, according to the CDC. One in four people infected with V. vulnificus die from their infection. From this reason, the FDA and the CDC have both created health education kits aiming at deterring people from ingesting raw oysters.
But Is There A Way to Be Safe? Can We Prevent Infection?
These education kits aim at dispelling common myths about the eating of raw oysters, such as the ability to identify “clean” oysters versus “polluted” ones (in fact, Vibrio bacteria are naturally occurring and are not a signal of water contamination). The organizations also warn that substances such as hot sauce or alcohol are not capable of neutralizing the effects of Vibrio. Additionally, the health kits warn that oysters with Vibrio do not taste any different than those without. Therefore both the CDC and FDA warn against eating raw oysters, noting that it is the only effective way to avoid contracting the illness.
Scientists are, however, looking into environmentally friendly ways to inhibit the growth of Vibrio bacteria in oysters. Preliminary research suggests that green tea extract, rich in phenolic components, significantly reduces contamination by Vibrio bacteria, according to Science News. Green tea’s antimicrobial properties could be useful in extending shelf life of refrigerated oysters.
Studies have also been conducted to explore grapeseed extract as a natural control for Vibrio in shucked oysters. Findings have suggested that the combination of citric acid and lactic acid present in grapeseed extract, along with its phenolic content, may inactive Vibrio, as noted in Food Control.
These inexpensive and natural options can aid in reducing food safety concerns for both industry and consumer. It is vital to note, however, that the goal of the studies was to examine ways to extend shelf life. Health agencies warn against the consumption of raw oysters as the dangers associated with Vibrio infection, especially V. vulnificus, can be life threatening. The CDC recommends only eating thoroughly cooked shellfish and to avoid consuming any oysters that do not open during cooking.