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If you were planning on a shore vacation this year, you might have kept track of great white sharks. The apex predator made famous by Jaws (and, OK, by The Meg and Sharknado) has been spotted on East Coast beaches from South Carolina up past Cape Cod, leaving potential beachcombers worried by accounts of close encounters and attacks.
But many marine biologists are worried about a much smaller—in fact, microscopic—threat. They are tracking an unprecedented surge in ocean-going bacteria known as Vibrio, which recently killed three people and sickened a fourth in Connecticut and New York, at least two of them after swimming in the coastal waters of Long Island Sound.
For swimmers and fishermen in the Gulf of Mexico, Vibrio is a known summer foe. It is one of the reasons for the old saying that you shouldn't eat oysters in months that don’t have an R in their name: Warmer water encourages bacterial growth, and oysters accumulate these organisms when they feed. The bacteria is also an infection hazard for anyone who gets a cut while cleaning up soaked debris after a hurricane. But Vibrio appearing in the waters of the upper East Coast is a new and unfamiliar problem, fueled by the rapid ocean warming of climate change.
Researchers worry Vibrio is going to become a persistent threat to whether people can safely enjoy the beach—and physicians who work in areas where it is already common wonder whether their northern colleagues will be alert to its potentially fatal risks. “We are used to certain diseases in our area, but they are something that clinicians in the Northeast, for example, may not be as familiar with,” says Cesar Arias, a professor and chief of infectious diseases at Houston Methodist Hospital. “All these changes in climate that we are seeing, including the tremendous heating of the oceans, is making the geography of infectious diseases change.”
Already, the Centers for Disease Control and Prevention estimates that there may be 80,000 illnesses and 100 deaths caused by Vibrio species in the US each year; about 52,000 of them come from eating seafood. But because shellfish safety is tightly policed by federal agencies, it’s the other portion of Vibrio infections, caused by the species Vibrio vulnificus, that is raising so much concern right now. These infections happen when bacteria-laden seawater infiltrates a break in the skin. In an average year there are believed to be 28,000 cases, but that’s widely considered an undercount.
Those infections can be treated, if people get antibiotics quickly. But without rapid attention, they can cause necrotizing fasciitis—flesh-eating disease—that can only be arrested by amputation, and also can put people into septic shock in as few as two days. The bacteria can enter the body through very minor injuries: a cut from stepping on a shell, a pinch from a crab’s claws, water touching the incision created by a new piercing or tattoo. Up to one-fifth of those who contract vibriosis from wound infections die.
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The risk is serious enough that, on Friday afternoon, the CDC sent out an alert to health departments and physicians, urging them to consider the possibility of V. vulnificus if they learn of wound infections in anyone who has been in the water in the Gulf of Mexico or on the East Coast. The alert emphasizes how fast these infections turn septic and asks doctors to send cultures to a lab—but it also urges them to start patients on antibiotics immediately, without waiting for lab results or consultation with a specialist.
Vibrio are on the move. In March, a research team based at the University of East Anglia in the United Kingdom used records of diagnoses combined with models of climate warming to define the situation in the US now and forecast what might come next. They found that, just for V. vulnificus wound infections, cases increased eightfold between 1988 and 2018. Every year, they were recorded about 30 miles (48 kilometers) further north.
Then, using several computer models based on predicted levels of greenhouse gas emissions combined with population movements, the group plotted the bacterium’s possible further shift. Under a conservative low-emissions scenario, they found that Vibrio—already present in the Chesapeake Bay—might extend its range to the middle of the New Jersey shore by 2060. In the outer bound of a high-emissions scenario, it might move as far north as the coast of southern Maine by 2100.
Elizabeth Archer, an environmental scientist who led the work as a doctoral student, says it was a mild shock to discover, via news of the recent Connecticut and New York cases, that V. vulnificus had already reached the edge of New England. “Our model had predicted that area to be in the main distribution of infections by mid-century,” she says. “So it was perhaps a bit surprising that it came so soon—but also not surprising, given the trends in ocean warming and air temperatures.”
In a few scientific circles, there has been concern for years that temperature anomalies are permitting Vibrio to surge out of its historic areas. Bacterial surges have been documented on the coasts of the Netherlands and Poland, and isolated from tidal flats in northern California—all places where the water ought to be too cold for Vibrio to grow. And over the past decade, Vibrio has increased in Atlantic coastal waters off Florida and the Carolinas, not only contaminating seafood but also posing a hazard to people who fish or boat in marshes and in-shore waterways.
This year, the unprecedented warming of ocean water, which fueled the rapid intensification of Hurricane Idalia the night before it struck Florida’s Big Bend, is changing marine environments all the way up the Atlantic Coast. Both Long Island Sound—where two of the Connecticut victims were apparently infected—and waters off New England have reached record-high temperatures in the past few years.
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“V. vulnificus is only active at a temperature that's above 13 degrees Celsius, and then it becomes more prevalent up until the temperature reaches 30 degrees Celsius, which is 86 Fahrenheit,” says Karen Knee, who is an associate professor and water-quality expert at American University and an open-water swimmer accustomed to ocean conditions. “I was looking at the sea surface temperature maps, and everywhere south of Cape Cod is getting into territory that's above 20 degrees Celsius, which is when [Vibrio] really starts to become more infectious. And that's most of the swimming waters on the East Coast.”
There’s more going on than just temperature shifts. Geoffrey Scott, the chair of environmental sciences at the University of South Carolina’s Arnold School of Public Health who leads a research consortium on oceans and climate change, says changes in water quality are whomping up Vibrio’s ability to cause severe illness. Those changes are driven by people relocating to coasts, which increases nutrient flows into the ocean via wastewater.
Vibrio used to be a late-summer hazard, but is now turning up earlier—and also later— in the year. “We've gone from them being mainly an issue from late July through early October, to being present April through November,” says Scott, who formerly supervised several coastal laboratories in the National Oceanic and Atmospheric Administration. “And in some cases, they have been seen overwintering in North Carolina, around the Outer Banks.”
To the problems of V. vulnificus being more virulent, in more places, for longer, you can add that more people may be exposed: first, because hot weather naturally sends more people to the beach, and second, because some of those people may not realize how vulnerable they are. “[Vulnificus] predominantly seems to impact people who have liver disease much harder than those who do not,” says Scott Roberts, an infectious-disease physician and assistant professor at the Yale School of Medicine. “And in general, being in an immunocompromised state. That could be from age, could be from chemotherapy, or if there's some sort of underlying disease.”
Many people won’t know they are in danger. Every state with a shellfish industry participates in the National Shellfish Sanitation Program run by the Food and Drug Administration, which dictates standards for every aspect of shellfish production, including screening for contamination by Vibrio. That’s out of self-interest: Any hint of the organism’s presence can shut down a state’s shellfish economy. (In fact, since the recent deaths, the home page of the Connecticut Department of Agriculture has been topped by a highlighted banner declaring “Connecticut shellfish have never been associated with Vibrio vulnificus infections.”)
But there’s no national program that can warn swimmers or surfers of Vibrio’s presence in the ocean; no testing regime like ones that look for coastal E. coli; no system of flags like the ones that announce strong surf and rip tides. These hazards are local knowledge, shared among people who have lived alongside them.
“People down here may have a buddy who got cut on a shell or while fishing, and their finger’s a little red and swollen, and somebody will be like, ‘Don't sleep on that. I had a buddy who waited till the next morning and he lost his hand,’” says Brett Froelich, a microbiologist and assistant professor at George Mason University in Virginia. “Other people in other locations don't know that. They will absolutely think, ‘Well, I hope it gets better in the morning,’ and in the morning, their hand is black.”
This poses a problem: How to make the public in newly endemic areas conscious of their new risks. No one—especially not researchers at publicly funded universities—wants to be perceived as hurting coastal tourism. “We don’t want to scare people away from beaches,” Froelich says. “You don't need to avoid [them]. You just need to be aware.”
