A deadly bacteria is creeping up the East Coast. How worried should you be?

On Pensacola Beach, Bailey Magers and Sunil Kumar presented an unusual sight. Bags filled with disinfectant surrounded them on the pristine white sand; their gloved hands adeptly handled test tubes, while layers of protective rubber and plastic insulated their skin from the outdoor elements. As the pair arranged their samples of seawater along the popular Florida coastline last August, an elderly woman in a swimsuit approached them, curious about their activities.

“We’re simply performing active water quality surveillance,” they informed her, but she pressed for more details.

“Are you investigating that flesh-eating bacteria?”

“That’s part of our focus,” they responded, careful not to alarm her. The woman, seemingly content with their answer, turned back towards the ocean. As she departed, Kumar observed that her body had several minor abrasions and bruises. Moments later, he watched her wade into the waves. He shivered slightly before refocusing on his work.

Magers and Kumar are engaged in the study of Vibrio, a genus of ancient marine bacteria believed to have originated during the Paleozoic Era. At that time, vast, shallow seas covered the Earth’s immense, interconnected landmasses, fostering complex marine ecosystems that thrived in these warm, newly formed aquatic environments. Today, hundreds of millions of years later, researchers estimate over 70 Vibrio species exist. These organisms inhabit warm, brackish waters, adhering to plankton and algae and concentrating within prolific filter feeders such as clams and oysters.

A select group of Vibrio species can cause illness and, in severe cases, be fatal. In dire circumstances, individuals exposed to the most hazardous strains — either by swimming in brackish water with an open wound or consuming raw shellfish tainted with the odorless and tasteless toxin — may face a rapid progression, with one or more limbs beginning to bruise, swell, and decompose within hours. Without prompt and potent antibiotic treatment, septic shock can occur, leading to death. While anyone can become infected, the risk is considerably higher for those with liver disease, compromised immune systems, the elderly, or diabetics.

The world’s oceans, having absorbed over 90 percent of the surplus heat from greenhouse gas emissions, are becoming increasingly favorable environments for Vibrio due to climate change. Studies indicate that temperature and salinity are the primary factors influencing the prevalence of Vibrio bacteria. As water temperatures rise, so does the concentration of Vibrio in marine waters, elevating the risk of infection for both beachgoers and shellfish eaters. The bacteria become active in water above 60 degrees Fahrenheit and proliferate rapidly as coastal waters warm throughout the summer months.

In recent years, researchers have observed Vibrio extending its habitat into areas previously too cold to sustain it, migrating as far north as Maine along the U.S. East Coast and becoming more common in temperate waters globally.

Overall, vibriosis infections represent the leading cause of shellfish-associated illness in the United States. Since the Centers for Disease Control and Prevention (CDC) began tracking such illnesses in 1996, they have increased “more than any other illness caused by a pathogen in the U.S. food supply,” according to a 2019 analysis by the International Association for Food Protection. This report attributed the sharp increase to a “perfect storm” of factors, including climate change, food handling practices, increasing globalization, inconsistent regulatory oversight, and improved diagnostic methods.

Through their noticeable fieldwork in Pensacola and other Florida coastal areas, Magers and Kumar aim to pinpoint where and when harmful Vibrio species are present throughout the state. Their research contributes to an ongoing initiative at the University of Florida, which seeks to establish a Vibrio early warning system for the eastern United States. This system would inform public health departments of elevated Vibrio concentrations in specific regions up to a month in advance.

Magers ponders how many limbs could be spared if medical professionals received timely alerts about an impending rise in these frequently underdiagnosed infections.

This research serves a dual purpose: As Vibrio bacteria migrate northward into colder waters, they act as an initial indicator of shifting marine conditions, signaling to scientists that the accustomed composition of local marine species may be undergoing transformation. For instance, in Europe’s Baltic Sea, a surge in Vibrio infections in July 2014 directly coincided with a heatwave that rapidly warmed the shallow body of water.

This event demonstrated to researchers that Vibrio spikes predict unusually warm marine conditions, leading to their subsequent use as indicators for ocean heatwaves and sea-surface warming trends, beyond just food safety.

“We consider Vibrio a proxy for climate change,” stated Kyle Brumfield, a microbiologist at the University of Maryland who has dedicated a decade to studying the bacteria. “The occurrence of Vibrio and Vibrio cases can be used to assess overall water health.”

The CDC estimates approximately 80,000 cases of vibriosis annually in the U.S., resulting in about 100 fatalities. The majority of these 80,000 cases are caused by *Vibrio parahaemolyticus*, which typically leads to gastroenteritis, or food poisoning. However, the overwhelming majority of deaths are attributable to *Vibrio vulnificus*—a name derived from the Latin for “wound-making.”

*Vulnificus* is so aggressive that it can penetrate a minuscule skin abrasion and cause death within 24 hours. Over the past five years, the CDC recorded 429 such *vulnificus* cases from water exposure, along with 136 foodborne cases. Despite foodborne cases being less frequent, patients who contract *vulnificus* from contaminated shellfish face a higher mortality risk than those infected through open wounds. Thirteen percent of non-foodborne cases resulted in death, compared to 32 percent of individuals infected by consuming seafood. Most incidents occur in the coastal regions of the Gulf and Atlantic.

In the realm of infectious diseases, *vulnificus* is exceedingly rare; the CDC reports between 150 and 200 cases per year. For context, chlamydia, a sexually transmitted infection and one of the most common bacterial infections in the U.S., affects over 1.5 million Americans annually. Yet, *vulnificus*’s alarming speed and high fatality rate — ranging from 15 to 50 percent, depending on the patient’s health and the infection route — establish it as a distinctive public health concern, especially as climate change expands potential exposure pathways.

*Vulnificus* is not a pathogen known for predictable behavior, yet that is precisely what it has been doing since the late 2010s. Along the Eastern Seaboard, both local and federal health authorities have been documenting “unusual surges” in *vulnificus* prevalence—sharp increases in infections that appear linked to extreme weather phenomena like hurricanes and marine heatwaves.

In 2022 and 2024, years marked by major hurricanes pushing brackish, Vibrio-friendly water inland, Florida’s public health department reported 17 and 19 deaths, respectively, associated with *vulnificus* exposure through open wounds. North Carolina, New York, and Connecticut also experienced localized outbreaks during a record-setting heatwave in the summer of 2023. “As coastal water temperatures increase,” the CDC cautioned in its analysis of these outbreaks, “*V. vulnificus* infections are projected to become more frequent.”

A 2023 research paper, which examined a 30-year dataset of confirmed *vulnificus* infections related to outdoor recreation along the U.S. Gulf and Atlantic coasts, revealed that the northern extent of infections has advanced by 30 miles annually since 1998. The study posited that “*V. vulnificus* infections may broaden their current range to encompass major population centers around New York,” and that annual case numbers could double as temperatures rise and America’s elderly demographic expands.

“In the 1980s, Vibrio populations would surge in late spring, remain high throughout summer, and then decline by mid-October,” noted Brumfield, whose Vibrio research is based in Maryland. “Now… we can detect them almost year-round.”

The level of concern warranted by the evolving behavior of Vibrio bacteria is subject to varying opinions and interpretations. The horrifying and rapid progression of *vulnificus* infections often makes them compelling material for local and national news outlets, leading to a flurry of alarming reports each time a new severe infection or fatality emerges.

“Virginia father wades in shallow water, succumbs 2 weeks later to flesh-eating bacteria that ‘devastated’ his legs,” announced a recent headline in People magazine. “Two deceased after consuming oysters, contracting flesh-eating bacteria, officials report,” stated a 2025 online article regarding two oyster-related deaths in Louisiana and Florida. Similar to many such stories, neither explicitly mentions the rarity of the bacteria.

This media coverage creates challenges for some segments of the seafood industry, which is not eager for a national discussion about the increase in vibriosis cases, particularly *vulnificus*. Shellfish farmers and industry representatives interviewed by Grist in Florida and New York contended that the media’s focus on the safety of their products is unwarranted. “‘Flesh-eating bacteria,’” remarked Leslie Sturmer, a researcher with the University of Florida’s shellfish aquaculture extension program who advises the industry on research and regulation — “the media sensationalizes it.”

Paul McCormick, an oyster farmer on Long Island who sells 750,000 oysters annually, believes any press is detrimental. “Even if your article is titled ‘New York oysters are the safest oysters on Earth,’” he explained during a phone call from his East Moriches office in January, “you’ve already created an issue.”