This story was produced by Grist and co-published with
States Newsroom.
It is part of the Grist series Vital Signs, exploring the ways climate change affects your health.
This reporting initiative is made possible thanks to support from the Wellcome Trust.
Last August, on the sandy shores of Pensacola Beach, Bailey Magers and Sunil Kumar stood out. Surrounded by bags of disinfectant and equipped with test tubes, their gloved hands were busy collecting seawater samples. An older woman, curious about their activities, approached them as they worked on the popular Florida beach.
“We’re just actively monitoring water quality,” they explained. But the woman had another question.
“Are you looking for that flesh-eating bacteria?” she inquired.
“We’re looking into it,” they responded, intending not to alarm her. Satisfied, she turned back to the ocean. As she left, Kumar noticed her scrapes and bruises, watching her step into the waves. Shaking off a chill, he returned to his work.
Magers and Kumar focus on a bacterium called Vibrio, a descendant of ancient marine species from the Paleozoic Era. These organisms thrived in vast, shallow seas that covered Earth’s interconnected supercontinents. Today, Vibrio species, numbering over 70, exist in warm, brackish waters, attaching to plankton and algae and accumulating in water-filtering creatures like clams and oysters.
While most Vibrio species are harmless, a few can cause serious illness or even death. Exposure through open wounds in brackish water or the consumption of raw, contaminated shellfish can lead to symptoms like bruising, swelling, and tissue decay within hours. Without prompt antibiotic treatment, septic shock and death can occur. Vulnerability is higher in individuals with liver disease, compromised immune systems, the elderly, and diabetics.
Climate change is making oceans more conducive to Vibrio growth, as they absorb over 90% of excess heat from greenhouse gas emissions. Research highlights temperature and salinity as key indicators of Vibrio prevalence. Rising water temperatures increase Vibrio concentrations in seawater, raising infection risks for beachgoers and shellfish consumers. The bacteria become active above 60 degrees Fahrenheit and multiply rapidly as coastal waters warm during summer.
Recently, Vibrio has been found in previously too-cold regions, reaching as far north as Maine along the U.S. East Coast and appearing more frequently in temperate seas globally.
Vibriosis infections are the leading cause of shellfish-related illnesses in the U.S., having increased “more than any other illness caused by a pathogen in the U.S. food supply” since the CDC began tracking in 1996, according to a 2019 analysis by the International Association for Food Protection. The report attributes this rise to a “perfect storm” of climate change, food handling practices, globalization, patchy regulatory oversight, and better diagnosis.
Through their research trips to Pensacola and other Florida beaches, Magers and Kumar aim to determine the presence and timing of harmful Vibrio species across the state. Their work supports a University of Florida initiative to establish a Vibrio early warning system for the eastern U.S., capable of alerting health departments a month in advance of high Vibrio concentrations.
Magers wonders how many limbs might be saved if healthcare providers knew in advance about potential increases in these underdiagnosed infections.
The research has dual purposes: As Vibrio extends into cooler waters, it signals changing marine conditions, alerting researchers to potential shifts in local marine species compositions. For instance, a Vibrio spike in the Baltic Sea during a July 2014 heatwave offered insight into unusually warm marine conditions.
This event demonstrated to researchers that Vibrio spikes indicate unusually warm marine conditions. They have since been used as barometers for ocean heatwaves and sea-surface warming patterns, beyond food safety.
“We see Vibrio as the indicator for climate change,” explained Kyle Brumfield, a microbiologist at the University of Maryland who has studied the bacteria for a decade. “We can use the presence of Vibrio and Vibrio cases as a proxy for water health in general.”
The CDC estimates that about 80,000 cases of vibriosis occur annually in the U.S., leading to approximately 100 deaths. Most cases are due to Vibrio parahaemolyticus, primarily causing gastroenteritis, or food poisoning. However, the majority of deaths result from Vibrio vulnificus, a name derived from Latin meaning “wound-making.”
Vulnificus is so potent it can enter through a pinhole-sized cut and cause death within 24 hours. Over the past five years, the CDC reported 429 vulnificus cases, with an additional 136 foodborne cases. While foodborne cases are fewer, those infected via shellfish consumption face a higher risk of death than those exposed through wounds. Thirteen percent of wound-related cases resulted in death, compared to 32 percent of those from seafood consumption. Most cases occur in the Gulf and Atlantic coastal regions.
Despite its rarity, with only 150 to 200 cases reported annually, vulnificus presents a significant public health threat due to its rapid progression and high fatality rate of 15 to 50 percent, depending on the individual’s health and infection route. Climate change exacerbates its spread.
Since the late 2010s, vulnificus has exhibited erratic behavior. Health officials along the Eastern Seaboard have noted “unusual increases” in prevalence, often linked to extreme weather events like hurricanes and marine heatwaves.
In 2022 and 2024, when major hurricanes pushed brackish water inland, Florida recorded 17 and 19 deaths, respectively, due to vulnificus from open wound exposure. North Carolina, New York, and Connecticut also reported small infection clusters during the 2023 summer heatwave. “As coastal water temperatures increase,” the CDC cautioned in its investigation, “V. vulnificus infections are expected to become more common.”
A 2023 study analyzing a 30-year database of confirmed vulnificus infections along the U.S. Gulf and Atlantic coasts found the infection’s northern boundary has shifted northward by 30 miles per year since 1998. The study suggested that “V. vulnificus infections may expand their current range to encompass major population centers around New York,” with annual cases potentially doubling as temperatures rise and America’s elderly population increases.
“In the 1980s, Vibrio abundance would increase in late spring, remain high through summer, and decline by mid-October,” noted Brumfield, a Vibrio researcher in Maryland. “Now, we can almost find them year-round.”
The extent of concern regarding Vibrio depends on perspective and media portrayal. The fast-acting and severe nature of vulnificus infections makes them sensational news material, often leading to alarming reports following any new severe case or death.
“Virginia dad wades in calf-high water, dies 2 weeks later of flesh-eating bacteria that ‘ravaged’ his legs,” read a recent headline in People magazine. “2 dead after eating oysters, contracting flesh-eating bacteria, officials say,” was the headline of a 2025 web story about two deaths related to oyster consumption in Louisiana and Florida. These stories often omit the rarity of the bacteria.
The seafood industry sees such coverage as detrimental, sparking unwarranted national debate on the safety of their products. Leslie Sturmer, a researcher at the University of Florida’s shellfish aquaculture extension program, remarked on the media’s fascination with “flesh-eating bacteria.”
Paul McCormick, an oyster farmer in Long Island selling 750,000 oysters annually, believes any press is detrimental. “Even if your article says ‘New York oysters are the safest oysters in the universe,’” he said from his East Moriches office, “you’ve already created a problem.”
Shellfish tags used to keep track of where and when shellfish is harvested.
Zoya Teirstein / Grist
A sign advertises oysters for sale in Cedar Key, Florida.
Zoya Teirstein / Grist
In warm conditions, unrefrigerated oysters allow Vibrio bacteria to reproduce every 20 minutes. However, in 2010, states implemented strict “Vibrio control plans,” mandating rapid cooling of catches on board and subsequent refrigeration at processing facilities within a specified timeframe. These measures have effectively halted Vibrio growth in harvested shellfish and prevented diseases.
Infections can result from either shellfish consumption or seawater exposure, making it easy to point fingers. Consumers have more control over Vibrio exposure than E. coli, for instance. Someone with a kidney condition can choose not to eat raw oysters, while E. coli, often found in raw vegetables, is more challenging to avoid. Similarly, individuals with open wounds can avoid bathing in brackish waters if they understand the risks.
For shellfish industry representatives, personal responsibility is key to reducing cases. “The person is the risk,” Sturmer stated. “Not the climate, not the water, not the bacteria.” This stance appears to align with the government’s position, as no numerical threshold exists for state public health agencies to close beaches for recreation. States may issue advisories and, on rare occasions, close beaches if they detect high Vibrio levels.
This perspective neglects the rapid marine changes caused by climate change, uneven awareness of vibriosis, and the fact that Americans often make health decisions contrary to their well-being.
