That’s where climate change comes in, making New England waters friendlier for the potentially deadly bacteria. “With warmer water temperatures moving further north, it allows Vibrios to survive, during summer months in particular, at higher latitudes than it had previously,” said Hamer.
And the water is warmer. Midsummer ocean temperatures were about 2.75 degrees warmer in the period from 2021 to 2025 than they were 20 years ago, according to data from an ocean temperature monitor in Woods Hole, near where the swimmer contracted the virus.
“A couple degrees difference will allow greater growth” of the bacteria, said Hamer. “And if it continues to rise, we’re going to see even more over the next five to 10 years.”
The oceans absorb more than 90 percent of the extra heat created by climate change, leading to sea level rise as water molecules expand and glaciers melt; supplying extra energy for hurricanes, which are fueled by heat at the surface of the ocean; and providing a more hospitable place for certain kinds of bacteria.
Scientists has been watching as Vibrio vulnificus infections have climbed northward as the planet warms. Between 1988 and 2018, wound infections from the bacteria increased eight-fold (from 10 to 80 cases per year) in the eastern United States, and the northern limit of reported cases moved north by roughly 30 miles each year, according to a 2023 study published in the journal Nature.
By the middle of this century, between 2041 and 2060, the authors of the study projected that Vibrio vulnificus would be occurring as far north as Boston, and found that in a scenario where the world does not sufficiently rein in greenhouse gas emissions, caused primarily by the burning of fossil fuels, it could extend into southern Maine toward the end of the century.
The good news is, as of now, this kind of infection is very rare in Massachusetts. The state has recorded seven cases of Vibrio vulnificus in the last several years, of which just four were likely exposed in Massachusetts. But Department of Public Health officials want to get the word out because, when people do contract an infection from the bacteria, the stakes are high.
One in five people with a Vibrio vulnificus infection die, sometimes within a day or two of getting sick, according to the Centers for Disease Control. Others may end up needing an amputation.
“There are increasing numbers of people who are immunocompromised by disease or by medication, and people in those categories are at higher risk of both contracting the disease and developing severe complications of the disease,” said Larry Madoff, medical director of the state Department of Public Health. “And this is the time of year, right? This is when the waters are warm and warming.”
Madoff warned that people with underlying medical conditions in particular should be cautious about swimming in the ocean if they have scrapes or cuts and eating raw or undercooked seafood, which is another way people can contract the bacteria.
“If I had a small scratch and I had bad liver disease, I would just stay out of the water,” Madoff said.
But he’s also not warning people away. “It’s a good way of staying cool. We don’t think people need to avoid the beach,” he said.
Sabrina Shankman can be reached at sabrina.shankman@globe.com.
