Flesh-eating bacteria are becoming more pervasive—here’s why
Climate change is creating the conditions for grisly pathogens like Vibrio to thrive in global waterways.
After scratching his leg on a boat trailer in Bay St. Louis, Mississippi a 77-year-old man died on July 21, 2025. The culprit behind the tragic progression of what seemed like a routine wound was an infection on his scratched leg, caused by bacteria Vibrio vulnificus. He’s one of several whose infection has recently made headlines.
The bacteria cause rapidly spreading skin blisters, which damage tissue and can quickly lead to sepsis, amputation, and even death. About 150 to 200 of these serious but rare infections occur in the U.S. annually, and one in five will die within just a few days of becoming infected, according to the Centers for Disease Control.
Better known as flesh-eating bacteria, V. vulnificus thrives in warm, brackish waters, where salt water and fresh water meet.
Cases used to occur primarily in southern waters along the Gulf coasts of Louisiana and Florida but are now being documented as far north as Connecticut, Massachusetts, and New York. Along both the Gulf and East coasts, documented infections have increased eightfold in the past 30 years.
“It’s the most expensive waterborne disease in the U.S. because it leads to amputation and death and medical treatment is always difficult,” says Jan Carlo Semenza, an epidemiologist at Umeå University in Stockholm, Sweden. In 2023, he authored a paper in The New England Journal of Medicine that highlighted the link between warmer temperatures and two species of Vibrio, the bacteria leptospira, and a parasite called cryptosporidium.
Semenza’s paper is part of a growing body of research showing how some water-dwelling pathogens are becoming more common and spreading to new reaches as global temperatures rise. Scientists also suspect that hotter temperatures are changing our risk exposure, creating a greater demand for air conditioning and more time spent in risky bodies of water.
Not only are waterborne diseases like Vibrio finding more hospitable environments, but they are also infecting a population that’s increasingly immunocompromised from chronic disease and less able to fight off infection, says John Sinnott, chairman of internal medicine at the University of South Florida College of Medicine and former director of the Florida Infectious Disease Institute.
Diabetes, for example, causes slow-healing wounds that are more vulnerable to infection. And those with chronic conditions like diabetes, cardiovascular disease, and cancer are also more susceptible to severe respiratory infections caused by the waterborne pathogen responsible for Legionnaires’ disease.
“These infections are rare but the fear from our side is that if water temperatures continue to rise, they’ll become more and more common,” says Daniel Egan, an infectious disease specialist at Orlando Regional Medical Center, in Florida.
Why do infections increase with warmer temperatures?
Over the past three decades, sea surface temperatures have risen dramatically and in 2024 the average global sea surface temperature was the highest on record, an increase linked to greenhouse gas in the atmosphere.
“There’s a direct relationship between an increase in sea surface temperature and an increase in cases,” says Semenza.
He’s particularly concerned with Vibrio bacteria that live in brackish waters where warm temperatures, moderate salinity, and nutrients in the water help bacteria replicate particularly fast. Brackish waters are also ideal habitat for shellfish like oysters, which can be infected with the bacteria and are a frequent culprit behind human infections.
While the bacteria are always present, a higher density of Vibrio in the water makes infection more likely. Their optimal temperatures range between 68°F and 95°F and as summer temperatures extend into the fall, the bacteria is able to thrive for longer. A report published in May of last year by the research group Climate Central found that, on average, cities around the world experienced an additional month of extremely hot days.
In addition to creating optimal conditions for bacteria to multiply, Semenza worries that more hot days will also drive people to spend time in water.
Prolonged hot temperatures can also shrink bodies of water, increasing the density of bacteria in the water that remains, says Semenza.
Several more commonly found species of Vibrio bacteria like Vibrio parahaemolyticus and Vibrio alginolyticus, are also being detected more frequently, causing symptoms ranging from gastrointestinal issues to fever and the skin infection cellulitis.
While Vibrio bacteria are common in brackish water along the coast, fresh water can also harbor grisly microbes.
Though it’s exceedingly rare, with only around ten cases annually in the U.S., exposure to the amoeba Naegleria fowleri is nearly always fatal.
Once it enters the nasal passages, N. fowleri travels by way of the olfactory nerve to the brain where it begins damaging tissue. The amoeba is extremely deadly because it’s not bacterial, so doctors can’t treat it with antibiotics.
Cases of this fatal amoeba have increased by 1.6 percent annually since 1965 around the world. The most recent case in the U.S. occurred over the Fourth of July holiday in South Carolina when a 12-year-old boy died after jumping into Lake Murray, a reservoir in the center of the state, and getting infected water up his nose.
(Learn more about how this amoeba is spreading around the world.)
How AC and natural disasters create more disease risks
Other waterborne illnesses like Legionnaires' disease, cause by the Legionella pneumophila bacteria, have seen marked increases in cases as temperatures rise. Once found primarily in cities in the northeast, Legionella is now found in the Midwest and is now contracted in hot fall months, in addition to summer. Infections have increased by over 84 percent since the early 2000s and kill around 10 percent of those infected.
Studies have shown that more rainfall, higher humidity, and higher temperatures can drive increases in Legionella bacteria in the water, but it’s most commonly contracted when an individual inhales contaminated mist from air conditioning cooling towers, hot tubs, saunas, pools, or splash pads.
In this case, exposure may increase as a result of more frequent air conditioning use or playing in pools, hot tubs, and splash pads for longer periods of the year, says Semenza.
“We get Legionnaire’s disease when we have to rely more on air conditioning, which is more prevalent when it’s hot,” says Semenza.
Early this summer, an outbreak of Legionnaires disease led to 114 confirmed cases in New York City, and was caused by contaminated mist from the cooling towers of large air conditioning units in East Harlem that can spread infected mist over miles.
In addition to an uptick in air conditioning, warming temperatures also make disasters more likely.
Powerful storms cause bodies of water to become cesspools of sewage and debris, says Egan, and research shows that the number of more intense hurricanes, those above a Category 3, have more than doubled in the past 40 years.
With debris and flooding, people end up trudging through bacterial-laden waters and if you have an open wound or you nick your foot on broken glass, you’re immediately susceptible to infection, says Egan.
How to protect yourself from waterborne diseases
For infections that occur in wounds, such as Vibrio, the easiest way to avoid them is to stay out of the water if you have an opening on your skin. If you do have an open wound that’s exposed, use soap and water to clean it, redress it every 12 hours with a fresh bandage, and don’t go back in the water until it’s healed, says Egan.
Local and state health departments often track and issue warnings around high levels of bacteria in certain bodies of water, especially during the hottest parts of the year. Check their websites for updates or follow them on social media. Be particularly careful in late July and August when the waters are warmest.
After a hurricane or major flood, don’t enter murky water where it’s difficult to see to the bottom—this makes it harder to avoid injury and waters will likely be polluted.
If you do get cut, be aware of general signs of infection like fever, chills, night sweats, fatigue, or a feeling of malaise. A wound may be infected if it’s red, warm, and oozes puss.
More serious infections likes V. vulnificus cause rapidly spreading redness around the site of the infection within a few hours and require an immediate trip to the emergency room.
