Calling it "flesh-eating bacteria" is technically inaccurate, but the nickname captures what it does: destroying tissue so fast that limbs have to be amputated within hours.
The popular term in fact covers several bacterial species capable of causing necrotising fasciitis, the progressive death of muscle and skin tissue. The two under closest scrutiny today 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 ways: when an open wound comes into contact with contaminated water, or through eating raw shellfish, especially oysters.
In healthy people, infection usually causes only gastrointestinal symptoms. The trouble starts in vulnerable groups: patients with liver disease, people with weakened immune systems, diabetes or advanced age. In them, the bacterium can trigger sepsis and tissue necrosis within 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 wounds in the skin, not through seawater. In its most dangerous form it causes streptococcal toxic shock syndrome (STSS), with a mortality rate of around 30%.
