Opinion | O, Lovely Oysters. What Can You Tell Us About Our Changing World?

Who hasn’t read Lewis Carroll’s ode in which sweet, young oysters leave their safe ocean-bed only to be eaten by a wily walrus and his dour human pal? Today, scholars still debate the meaning behind “The Walrus and the Carpenter,” at times alleging that the gluttonous pair were proxies for 19th-century power and greed.

Like most children, what grieved me most when reading the Victorian-era verse was the oysters’ terrible end. Plus, who in their right mind ate oysters anyway? Talk about slimy and gross.

Fast forward a couple decades and I’d crossed the Rubicon. I came to adore oysters. Oysters Rockefeller. Steamed oysters with ginger and scallions. And best of all: raw, briny oysters with a dash of Tabasco, lemon juice, or a delicate mignonette.

I wasn’t even perturbed by a late 1980s study linking oyster intake, intestinal symptoms, and Vibrio stool cultures in roughly 500 doctors and scientists visiting New Orleans. Yes, those who ate oysters — both raw and cooked — suffered more diarrhea than those who abstained. On the other hand, since more than half of the subjects who passed non-cholera Vibrios in their stool never fell ill, why all the fuss?

Then, in 1995, the FDA approved the first-ever Hepatitis A vaccine. What a boon, especially for people who loved filter-feeding bivalves like oysters, mussels, scallops, and clams, as well as many others at risk for Hepatitis A’s harshest blows (think citrine conjunctivae, hemorrhage, encephalopathy), which were all too common in my early-career days.

Finally, consider norovirus, one more enteric blight that now infects 20 million Americans every year, especially in winter. True to form, norovirus once again surged this season and caused violent emesis and intestinal flux in many U.S. residents, among whom were more than 80 oyster devotees attending a high-end food fest in Los Angeles.

And just to be clear: those lovely, tainted oysters served at the L.A. Times‘s annual “101 Best Restaurants” gala came from northern waters far more frigid than the Louisiana Gulf.

Uncomfortable Truths About Vibrios

Now, let’s dive deeper into Vibrios — motile, comma-shaped bacteria that live in brackish coastal water and sometimes contaminate oysters. Although Vibrio cholerae is the clan’s most infamous species, at times, Vibrio vulnificus emerges as another terrifying foe.

Picture this scene from the 1990s: a Hispanic-American family enjoying fresh oysters from a southern California vendor. But 24 hours later, one middle-aged woman was in an ICU fighting for her life while the rest of her relatives remained well. Biliary cirrhosis was the unique risk factor that underlay her sudden brush with death, while V. vulnificus was the perp that caused the profound sepsis and necrotic, blistering wounds for which she later received multiple skin grafts.

In fact, well before her fateful meal, this patient knew her diagnosis and was receiving excellent care. Her doctors’ sole oversight? They never told her to avoid raw or undercooked seafood.

Around the same time, a flurry of illness due to oysters carrying V. vulnificus attacked or killed other Angelenos with pre-existing liver disease. This, in turn, prompted public health authorities to launch county-wide education, including Spanish-language posters in stores selling seafood. Ever since then, the U.S. has witnessed both a steady rise and geographic expansion of severe V. vulnificus infections acquired either from food or skin wounds exposed to warming coastal waters. And this infection is not one to toy with: V. vulnificus wound infections due to seawater exposure carry an 18% mortality rate.

Now to Vibrio parahaemolyticus, another burgeoning risk to people, both healthy and ill, who consume filter-feeding bivalves harvested from as far north as British Columbia. Although less lethal than V. vulnificus, this species also causes gastroenteritis, wound infections, and sepsis mediated by a thermo-stable toxin found in strains sickening humans.

A final clinical pearl from a recent report from Australia about oyster-related V. parahaemolyticus infections in 268 people with a median age of 52: in this outbreak, many sufferers were on drugs that reduce gastric acid — a timely reminder that hypochlorhydria (which increases with age even in unmedicated people) predisposes us not just to infections due to Vibrios but other gastrointestinal pathogens as well.

Of Sewage Spills and Warming Waters

“The time has come,” the Walrus said, “To talk of many things.”

Well, to be perfectly frank, the time has come to confront the elephant in the room: the impact of warming marine waters plus severe weather events on certain seafood-related infections. Because truly making this case requires integrating bacteriologic, environmental, meteorological, and medical data, I recommend a recent comprehensive review that correlates climate change and a global view of the rising incidence of illness due to different pathogenic Vibrios. One striking statement by its authors? “In the eastern United States, the incidence of V. vulnificus infection, one of the most pathogenic forms of Vibrio spp., has increased more than 8-fold from 1988 to 2018, with case numbers projected to double by 2100.” In recent years, similar trends have been noted with respect to V. parahaemolyticus and cholera.

On the other hand, a different environmental truth applies to viruses concentrated in tasty molluscan shellfish. Unlike Vibrio bacilli, which naturally inhabit seawater, norovirus and hepatitis A enter oceans via human sewage (or in some cases, vomit) originating from faulty septic systems or wastewater treatment plants, as well as boaters and beach-goers.

Long story short: not all modern bivalve-borne infections can be blamed on climate change as opposed to human feces sullying our seas. In addition, other lapses in handling can lead to contamination by conventional food-borne baddies like Salmonella and E. coli.

So, where does this leave certain oyster-lovers, myself included?

Even though rapid, post-harvest cooling and other modern strategies — such as thermal processing, freezing, irradiation, high-hydrostatic pressure, and high-salinity relaying — may someday mitigate the microbial risks of uncooked shellfish, I’ve once again changed my tune.

For now, no more raw oysters for me.

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