Climate experts have long warned about the myriad ways that warming temperatures can negatively affect human health. Now that global temperatures are predicted to increase by 1.5°C by the 2030s, that risk is becoming increasingly real.
One long-held prediction that appears to be coming true—according to the results of a new study—is how climate change can potentially expand concentrations of bacteria that thrive and spread through warm U.S. waters and cause an infection with a particularly high fatality rate.
In a paper published in Nature Scientific Reports, scientists at the University of East Anglia in the U.K. analyzed infections that were reported to the U.S. Centers for Disease Control and Prevention (CDC) from 1988 to 2018 caused by Vibrio vulnificus, a type of bacteria that lives in sea or brackish waters warmer than 68°F. Vibrio vulnificus kills approximately 20% of the healthy people, and 50% of those with weakened immune systems, that it infects—though it’s rare in the U.S. (for now). People can get infected either by eating raw shellfish such as oysters or by exposing small cuts or wounds to waters where the bacteria live; eating infected shellfish can cause diarrhea vomiting, fever and chills, while infected wounds can lead to serious skin infections. There is no strong evidence that antibiotics can control the infection, but doctors may prescribe them in some cases.
The researchers focused on wound-based infections, since those are easier to pinpoint to specific locations. They then created models predicting the pattern of new infections over the next few decades. One model assumed a more sustainable trajectory, in which emissions would be relatively low and the rise in global temperatures would be slower. Another assumed more of a worst-case scenario, in which containing emissions and addressing warming were low priorities for nations around the world.
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In the first model, the scientists concluded that Vibrio vulnificus infections would likely extend as far north as Connecticut as soon as half a century from now, in 2081. Under the latter model, these infections would be be reported in every eastern U.S. state by then. Currently, only about 80 cases are reported in the U.S. each year; by 2081, that could jump to anywhere from 140 to 200 cases under the worst-case scenario, the authors say. Current trends, they add, are somewhere between the two ranges they used.
Those cases would be the result of a continued northward creep of Vibrio vulnificus infections, extending from the Gulf coast, where infections have historically been concentrated, all the way to the waters off of Pennsylvania and New Jersey, where infections have been reported since 2018. This expansion represents not just outlier cases, but the concentration of cases, which is increasingly moving higher up the coastline as temperatures warm. “We’re seeing the core distribution of infections extending to areas that traditionally have very few and very rare cases,” says Elizabeth Archer, a PhD researcher in the School of Environmental Sciences and the lead author on the study. “But these areas are now coming into the main distribution of infections.”
The reason why has to do not only with warming sea temperatures but warming air temperatures as well, which are drawing more people to the coasts and bays and into contact with the bacteria.
“The bacteria are part of the natural marine environment, so I don’t think we can eradicate it from the environment,” says Archer. “It’s more about mitigating infections by increasing awareness and improving education about the risk. That means having more tools to alert people if there are particularly high concentrations in certain areas on particular days.”
The National Centers for Coastal Ocean Science, part of the National Oceanic and Atmospheric Administration, for example, has developed models to estimate changing concentrations of Vibrio vulnificus in the Chesapeake Bay, Delaware Bay, Gulf of Mexico, and other coastal areas. The models are still for research purposes, but they’re a starting point for future ways to track and alert people about bacterial surges that could pose a health risk. The European Center for Disease Control and Prevention has a tracker that provides six-day information on Vibrio vulnificus concentrations in waters in the region. “We need bigger geographical areas covered by these tools in order to visualize where the risk might be occurring in the near future,” says Archer.
Ultimately, what would help to curb Vibrio infections is an index that would allow the public to monitor Vibrio levels similar to the way people currently have information about air quality. “Just as we currently have pollen alerts, there could be something similar with Vibrio,” says Iain Lake, professor of environmental epidemiology at University of East Anglia and senior author of the paper. He notes that the bacteria are so sensitive to temperature changes that concentrations could bloom even after a day of warmer water, so consistent monitoring and alerts are critical.
Lake says the expansion of Vibrio vulnificus is concerning for public health since the bacteria is now invading waters closer to heavily populated areas, such as New York and Philadelphia. “Everyone can get a Vibrio vulnificus infection,” he says. “But the more interaction there is between warmer waters and people, the more the bacteria can move into populations such as the elderly and those with other health conditions, who are more vulnerable to infections.”
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