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A potentially very strong El Niño could help create conditions that favor Vibrio vulnificus, a dangerous bacterium linked to severe infections, but experts cautioned that the climate pattern should not be directly tied to case numbers on its own.
The discussion comes after at least six people have died in Louisiana and Florida this year from infections linked to the so-called "flesh-eating" bacteria, while cases and health alerts have emerged in multiple states.
What Is El Niño?
El Niño is a recurring climate pattern marked by unusually warm sea surface temperatures in the central and eastern equatorial Pacific Ocean. It can shift weather patterns around the world, influencing rainfall, winds, storm activity and temperatures, although its effects vary by region and from one event to another. Meteorologists generally use the informal term "super El Niño" to describe exceptionally strong El Niño events.
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The latest update from NOAA’s Climate Prediction Center, issued July 9, said an El Niño Advisory remained in effect and that the event was strengthening. CPC said there was an 81 percent chance of a "very strong" El Niño during October to December 2026, which it said would rank among the largest El Niño events in records going back to 1950. It also said there was a 97 percent chance El Niño would continue through early spring 2027.
Could Super El Niño Impact Vibrio Vulnificus Cases?
Craig Baker-Austin, a research microbiologist at the U.K.’s Centre for Environment, Fisheries and Aquaculture Science, told Newsweek that El Niño may raise risk by changing the coastal conditions in which V. vulnificus can grow.
"El Niño has the potential to increase Vibrio vulnificus risk indirectly by modifying coastal environmental conditions that favor the bacterium," Baker-Austin said.
He said V. vulnificus thrives in warm, brackish waters, especially when sea surface temperatures are elevated and salinity falls within a suitable range. Studies from the Gulf of Mexico and Chesapeake Bay, he said, have shown strong links between warmer water temperatures and higher abundance of the bacterium, as well as human infections.
"During El Niño years, sea surface temperatures can be higher than average in parts of the U.S. coastal zone, while changes in rainfall, river discharge and storm activity may alter coastal salinity," Baker-Austin said. "These environmental changes can increase habitat suitability for V. vulnificus, potentially extending the seasonal window of risk and increasing bacterial concentrations in estuaries and coastal areas."
He added that human behavior could also matter, because people are more likely to enter the sea when it is warmer, increasing opportunities for exposure.
"It is worth noting that global sea surface temperatures are among the hottest they have ever been," he said.
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Baker-Austin said the Gulf Coast remains the region of greatest vulnerability, naming Florida, Louisiana, Texas, Mississippi and Alabama as states with the warm temperatures and brackish estuarine conditions that support V. vulnificus growth. Those areas, he said, "tend to account for the majority of reported U.S. cases."
But he said the Atlantic seaboard is becoming more important as coastal waters warm. Infections are increasingly being reported in Mid-Atlantic and Northeastern states, including North Carolina, New York and Connecticut, he said, adding that climate-driven expansion of suitable habitat is projected to continue through the century.
David Fisman, a University of Toronto epidemiology professor at the Dalla Lana School of Public Health, said warmer water directly increases the abundance of the bacteria.
"Vibrios are thermophilic…that is, warmer water directly increases the abundance of the bacteria," Fisman told Newsweek. "So folks will contact higher bacterial loads wading or swimming, and levels of foodborne contamination in seafood will predictably rise."
However, Fisman said the largest increases in risk may occur in places where non-cholera vibriosis has historically been less common because waters were colder, such as the Pacific Northwest, British Columbia and Alaska. Louisiana and Florida, he said, are "classic locales" for the bacterium, so warming may "move the needle much less there."
Jaime Martinez-Urtaza, professor of genetics at the Autonomous University of Barcelona, also urged caution about drawing a straight line between El Niño and V. vulnificus cases.
"El Niño's main oceanic influence is on the Pacific coast, with a comparatively weak effect on local Gulf/Atlantic coastal waters," he told Newsweek.
The Gulf and Atlantic coasts, he added, do not have a direct oceanic pathway from the tropical Pacific, meaning any sea-surface temperature changes there during El Niño would be indirect.
Martinez-Urtaza said an elevated risk is plausible along the Pacific coast and, more indirectly, the Gulf Coast, but "the magnitude remains genuinely uncertain." He also said El Niño’s effect on hurricanes could complicate the picture: fewer storms could reduce storm-associated wound outbreak clusters, like those associated with Hurricanes Ian and Helene in 2022 and 2024, respectively.
What Is Vibrio Vulnificus and Who Is at Risk?
Vibrio bacteria naturally live in coastal waters and are found in higher numbers from May through October, when water temperatures are warmer, according to the CDC. People can get vibriosis by eating raw or undercooked shellfish, especially oysters, or when an open wound comes into contact with salt water or brackish water.
The agency says V. vulnificus can cause severe, life-threatening infections. Some patients need intensive care or limb amputation, and about one in five people with this infection die, sometimes within a day or two. People at higher risk include those with liver disease, cancer, diabetes, HIV, thalassemia, weakened immune systems, reduced stomach acid or recent stomach surgery.
Contact Newsweek editors on this story: Matthew Robinson and Tony Phillips.
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