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 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%.
