Hundreds have died in recent outbreaks of the so-called 'flesh-eating' bacteria Vibrio vulnificus and Streptococcus A. Driven by warming seas, Vibrio could spread across the Mediterranean by 2026 and has been killing silently for decades.
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.
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The popular label actually covers several bacterial species capable of causing necrotising fasciitis, the progressive destruction of muscle and skin tissue. The two currently most closely monitored are Vibrio vulnificus, which lives in the sea, and group A Streptococcus pyogenes, which spreads from person to person.
Vibrio thrives in warm, brackish waters, where rivers flow into the sea, and reaches humans in two main ways: when an open wound comes into contact with contaminated water, or through eating raw shellfish, especially oysters.
In otherwise healthy people, infection is usually limited to gastrointestinal symptoms. The problem arises in vulnerable groups: patients with liver disease, people with weakened immune systems, diabetics or older adults. In these cases the bacterium can trigger sepsis and tissue death within hours. According to the US Centers for Disease Control and Prevention (CDC), one in five patients with a severe infection dies within a few days.
Streptococcus pyogenes behaves very differently. It is transmitted via respiratory droplets or through skin wounds, not by seawater. In its most dangerous form it causes streptococcal toxic shock syndrome (STSS), with a case fatality 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 sharply in recent years. The two bacteria share the same nickname, but their transmission routes and risk profiles are different.
The latest outbreaks: from Florida to Japan via the Mediterranean
The recent track 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 concentrated along the southern coast, particularly in Florida and Louisiana, where the climate is ideal for its spread. 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. The total number of deaths linked to Vibrio in Florida that year reached 89, according to the state Department of Health.
The year 2025 was no better. By August, Florida had registered 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 US in just the first few months of that year.
In Asia, the main concern has been different. In Japan, cases of streptococcal toxic shock syndrome caused by Streptococcus pyogenes reached 941 in 2023, a record high. In 2024 that figure was surpassed in barely six months: Japan’s National Institute of Infectious Diseases confirmed 977 infections before the year was even half over, with 77 deaths recorded. The country had been reporting between 100 and 200 cases of this disease a year since 1992, which makes the recent figures particularly striking.
Europe, for its part, is confronting the problem from the marine side. Between 2014 and 2017, the average annual number of Vibrio infections on the continent stood at 126. In 2018, an exceptionally hot summer tripled that figure to 445 cases, mainly in Baltic countries: Norway, Sweden, Denmark, Finland, Poland and Estonia.
In June 2026, as summer began, it marked the start of a season that the European Centre for Disease Prevention and Control (ECDC) was already describing as high-risk. Spain is not starting from scratch: Galicia has recorded three significant outbreaks involving Vibrio species in the past two decades – 64 cases in 1999, 80 in 2004 and nearly 100 in 2012 – all linked to the consumption of local shellfish.
Heat as an ally: a threat that rises with the thermometer
The most pressing question is not just how many people have died, but why the numbers keep climbing. A large part of the answer lies in water temperature. Bacteria of the Vibrio genus thrive in moderately salty waters between 20 ºC and 35 ºC.
Those conditions, once confined to tropical and subtropical coasts, now extend every summer to latitudes that 30 years ago were far 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 are recorded.
The European Environment Agency estimates that sea-surface temperatures in European waters have risen between four and seven times faster than the global ocean average. The Mediterranean, seen by scientists as one of the regions most vulnerable to global warming, is particularly conducive to this. And it is not just about temperature: as heat shrinks bodies of water, bacterial density increases in what remains, raising the risk of exposure.
In July 2024, the European Food Safety Authority (EFSA) published a comprehensive risk assessment of these bacteria and its conclusion was clear: their prevalence in shellfish is expected to increase, in Europe and worldwide, as a consequence of climate change.
This projection also includes the geographical spread of the bacterium to coastal areas where it is barely detected today. The ECDC, for its part, has developed a surveillance system based on satellite data on sea temperature and salinity, which produces real-time risk maps to guide national alerts.
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. Globally, Vibrio infections have risen by more than 84% since the early 2000s, according to consolidated data. If the trend does not change, what is now a sporadic, seasonal risk could turn into a structural public-health problem in the medium term.
