Cases of a potentially fatal infection from a seawater-borne pathogen have increased off the U.S. Atlantic coast as ocean waters warmed over the last 30 years, and are expected to rise further in future because of climate change, according to a study published on Thursday by Scientific Reports, an open-access journal for research on the natural sciences and other topics.

The incidence of infections from Vibrio vulnificus, a pathogen that thrives in shallow, brackish water, was eight times greater in the eastern U.S. in 2018 than it was in 1988, and its range shifted northward to areas where waters were previously too cold to support it, according to the paper, “Climate Warming and Increasing Vibrio Vulnificus Infections in North America,” by academic researchers in the U.S., England and Spain.

By the middle of the 21^st century, the pathogen is expected to become more common in major population centers, including New York City, and by the end of the century, infections may be present in every U.S. Atlantic coast state if carbon emissions follow a medium- to high-level trajectory, the report said.

Infections can enter the body through skin wounds or by eating raw or undercooked shellfish, and can turn necrotic in as little as one or two days. That requires, in about 10 percent of cases, the surgical removal of infected flesh or the amputation of limbs. The mortality rate is as high as 18 percent, and fatalities have occurred as soon as 48 hours after exposure, the report said.

“Our projections indicate that climate change will have a major effect on V. vulnificus infection distribution and number in Eastern USA, likely due to warming coastal waters favoring presence of bacteria and elevated temperatures leading to more coastal recreation,” the study said.

Between 1988 and 2016, there were about 1,100 wound infections from V. vulnificus reported throughout the U.S., including 159 associated fatalities, highlighting “the significant yet underappreciated impact of this pathogen,” the study said.

By the middle of the century, the annual cases are projected to more than double to 145 from 61 between 2007 and 2018, based on a relatively low-emissions scenario. And by the end of the century, researchers predicted more than 200 cases a year.

The climate scenarios are expressed as “Shared Socioeconomic Pathways” (SSPs), which combine trends such as economic growth, population change and urbanization, with Representative Concentration Pathways (RCPs) that describe projected scenarios for carbon emissions. The combination of the two measurements allowed the influence of climate change in the distribution of V. vulnificus to be assessed.

A low-emissions, or “sustainable” scenario contrasts with one in which “resurgent nationalism and regional conflicts” detract from climate mitigation, resulting in medium- or high-carbon emissions, and a consequent warming of ocean waters.

James Oliver, a biology professor at the University of North Carolina, and one of nine co-authors, said that despite the increasing occurrence shown by the paper, the incidence remains low. But if an infection occurs, a patient should quickly get treatment. “Speed then is of the essence,” he said.

Oliver said the only way to slow the spread of the pathogen is by trying to curb climate change. “This pathogen needs lower salinity and warmer waters, both enhanced by global warming,” he said.

Cases of infection are already spreading northward. In the late 1980s, infections were rare north of Georgia but by 2018, they were regular as far north as Philadelphia, the report said. On average, the infection distribution has been shifting northward at 48 kilometers  per day over the study period.

At the same time, warming oceans extend the length of the Atlantic coastline, where conditions will be suitable in coming decades. By 2041-2060, the length of coastline where conditions would allow the pathogen to thrive would be 1,000 kilometers longer than in the study period, from 2007-2018. 

Combined with a growing population and an increasing number of elderly people—who are more susceptible to infection—the overall risk of infection doubles by the middle of the century, notably in the densely populated areas of New York and New Jersey.

The U.S. Centers for Disease Control and Prevention, in its own advisory on V. vulnificus, warns that infections can result from the pathogen entering an open wound when exposed to seawater, or from seafood juices dripping into it. Some of the infections lead to necrotizing fasciitis, a severe infection in which the flesh around an open wound dies. Such cases have led some media reports to call V. vulnificus “flesh-eating bacteria,” although that condition can also be caused by other kinds of bacteria, the CDC said.

Anyone can get a vibrio infection, but those with existing conditions such as liver disease, or those taking medications that lower the body’s immune response, are more susceptible, the federal health agency said.

It urged people with wounds including surgical incisions or piercings to stay out of salt water, to cover wounds with waterproof bandages, and to wash any wounds with soap and water if they are exposed to saltwater.

In 2019, Cooper University Health Care, a health system in southern New Jersey, reported five cases in the previous two years among people who had been exposed to water or seafood in the nearby Delaware Bay.

One victim died; one had his hands and feet amputated, and others had areas of their flesh surgically removed to prevent the infection spreading. The five cases in the summers of 2017 and 2018 represented a sharp increase from the single case that doctors from that system had treated in the previous eight years.

Each of the patients treated by Cooper had underlying health conditions including hepatitis, diabetes, morbid obesity and Parkinson’s disease, and so were much more susceptible to the infection than healthier people.

The patient who died, a 64-year-old man with untreated hepatitis C, presented with rapidly worsening pain and swelling in his right hand two days after cleaning and eating crabs caught in the bay. Surgeons removed areas of infected flesh three times, but the patient later died from ventricular tachycardia, an abnormally fast heart rate, the Cooper report said.

The patient who had his hands and feet amputated ate a dozen crabs the day before admission to the hospital and had been crabbing in the bay multiple times in the week before. Doctors said he didn’t immediately report his symptoms.

Dr. Henry Fraimow, an associate professor of medicine at Cooper Medical School of Rowan University, said the report underlined the findings by the Cooper report in 2019 that the number of V. vulnificus cases had increased in the Delaware Bay off southern New Jersey.

“It validated what we had shown, that the range of these organisms has clearly evolved,” he said. “We are finding these in places where they just didn’t happen before. As infectious disease physicians, we are well aware that the world is a changing place.”

Fraimow, one of the authors of the 2019 report, said other infections, such as those carried by ticks, are also showing up in areas where they were previously unknown, and which appear to be driven by climate change.

“This is not the only infection that is showing up in places where we didn’t used to see them,” he said. “It is hard to demonstrate causality but the northward shift of the range of many of these things, you can explain it however you want, but you have to think that climate change is playing a role.”

In 2010, researchers at the University of Bath in England reported a seasonal increase in V. vulnificus infections associated with eating oysters in the Gulf of Mexico, and said those cases correlate to higher water temperatures.“This retrospective review indicates that climate anomalies have already greatly expanded the risk area and season for vibrio illnesses and suggest that these events can be forecasted,” the Bath report said then.