Calling it a "flesh-eating bacterium" is technically inaccurate, but the nickname does capture what it does: destroying tissue so fast that limbs have to be amputated within hours.
The popular label actually covers several bacterial species capable of causing necrotising fasciitis, the progressive death of muscle and skin tissue. The two most closely monitored today are Vibrio vulnificus, which lives in the sea, and group A Streptococcus pyogenes, which spreads from person to person.
Vibrio lives in warm, brackish waters, where rivers flow into the sea, and reaches humans in two ways: when an open wound comes into contact with contaminated water, or through eating raw shellfish, especially oysters.
In healthy people, infection usually causes nothing more than gastrointestinal symptoms. The problem arises in vulnerable groups: patients with liver disease, people with weakened immune systems, diabetics or the elderly. In their case, the bacterium can trigger sepsis and necrosis in a matter of hours. According to the United States Centers for Disease Control and Prevention (CDC), one in five patients with a severe infection dies within a few days.
Streptococcus pyogenes has a different biology. It is transmitted via the respiratory route or through skin wounds, not through seawater. In its most dangerous form it causes streptococcal toxic shock syndrome (STSS), with a mortality rate of around 30%.
Although it has been known for decades and responds well to antibiotics such as penicillin or amoxicillin, the number of severe cases has risen strikingly in recent years. The two bacteria share the same nickname, but their routes of transmission and risk profiles are different.
RelatedThe most recent outbreaks: from Florida to Japan via the Mediterranean
The recent record of Vibrio vulnificus in the United States is the best documented in the world. Since 1988, the country has recorded more than 2,600 infections and over 700 deaths linked to this bacterium.
Cases are clustered along the southern coast, particularly in Florida and Louisiana, where the climate is ideal for it to thrive. In 2024, when Hurricane Helene struck in September, coastal flooding sent infections soaring: Florida reported 82 cases and 19 deaths, record figures according to state authorities. Over the year as a whole, Vibrio-related deaths in Florida reached 89, according to the state Department of Health.
The year 2025 was no better. By August, Florida had recorded 13 cases and 4 deaths, while Louisiana, where the historical average rarely exceeded one death a year, reported 17 hospitalised cases and another 4 deaths, a 400% increase in fatalities compared with previous years.
The most recent case occurred on 21 July 2025, when a 77-year-old man died in Bay St. Louis, Mississippi, after becoming infected through a scratch on his leg while working with a boat trailer. In all, eight people died from this bacterium in the United States in just the first months of that year.
In Asia, the source of concern was different. In Japan, cases of streptococcal toxic shock syndrome caused by Streptococcus pyogenes reached 941 in 2023, a record high at that point. In 2024 that figure was surpassed in barely six months: Japan’s National Institute of Infectious Diseases confirmed 977 infections before the year was half over, with 77 deaths recorded. The country had been registering between 100 and 200 cases of this disease a year since 1992, which makes the recent figures particularly striking.
Europe, for its part, is dealing with the problem from the marine side. Between 2014 and 2017, the continent recorded an average of 126 Vibrio infections a year. In 2018, an exceptionally hot summer tripled that to 445 cases, mainly in Baltic countries: Norway, Sweden, Denmark, Finland, Poland and Estonia.
In June 2026, as summer began, the European Centre for Disease Prevention and Control (ECDC) was already warning that the season carried a high level of risk. Spain is not starting from scratch: Galicia has seen three significant outbreaks caused by Vibrio species over the past two decades: 64 people affected in 1999, 80 in 2004 and almost 100 in 2012, all linked to the consumption of contaminated local seafood. There were no deaths in those outbreaks.
Heat as an ally: a threat that grows with the thermometer
The most pressing question is not just how many have died, but why the numbers keep rising. The answer lies largely in water temperature. Bacteria of the genus Vibrio thrive between 20°C and 35°C in waters with moderate salinity.
Those conditions, once confined to tropical and subtropical coasts, now extend every summer to latitudes that 30 years ago were too cold for this microorganism. Jan Carlo Semenza, an epidemiologist at Umeå University in Sweden, has documented this direct correlation: the higher the sea surface temperature, the more infections occur.
The European Environment Agency estimates that sea surface temperatures in Europe have been rising between four and seven times faster than the global average for the oceans. The Mediterranean, which the scientific community regards as one of the regions most vulnerable to global warming, is particularly at risk. And not only because of temperature: as bodies of water shrink due to heat, bacterial density in what remains increases, raising the risk of exposure.
In July 2024, the European Food Safety Authority (EFSA) published a comprehensive assessment of the risks posed by these bacteria and its message was clear: their prevalence in seafood is expected to increase, in Europe and worldwide, as a consequence of climate change.
This projection includes the geographical spread of the bacterium to coastal areas where it is currently scarcely detected. The ECDC, for its part, has developed a monitoring system based on satellite data (source in Spanish) on sea temperature and salinity that produces real-time risk maps to guide national alerts. Current hotspots are expected mainly in the Black Sea, the North Sea and the Baltic.
The impact is not only on health. Hatim Aznague, Climate Action and Energy Resilience analyst at the Union for the Mediterranean, sums it up neatly: "The bacteria are not the story; they are the messengers. The story is a sea thrown out of balance by heat and pollution". A beach closed in high season means immediate economic losses for hotels, restaurants and tour operators.
The Mediterranean is the world’s most visited holiday region, which magnifies the impact of any health alert. Vibrio infections have risen by more than 84% worldwide since the early 2000s, according to consolidated data. If the trend does not change, what is now a seasonal, localised risk could become a structural public health problem in the medium term.
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