With often terrible disfigurements, sometimes including the loss of limbs and in the worst case deaths being described within 24 hours in otherwise healthy people, I expect we've all heard of the flesh eating disease necrotising fasciitis or sometimes 'gas gangrene'.
Allen Cheng, Professor in Infectious Diseases Epidemiology, Monash University provides an overview here:
How is it contracted?
As with many infectious diseases, three factors interact to produce an infection: factors related to the bacteria; factors related to the patient; and factors relating to the environment that brings them together – in this case, the nature of the injury.
Patient factors associated with infection include impaired immunity (my emphasis), obesity and chronic diseases such as diabetes.
Many patients report a preceding breach in the skin, through things such as surgery, accidental wounds, or intravenous drug use.
Some types of infections are associated with particular settings. For instance, injuries occurring in marine environments, such as coral cuts, can be associated with particular types of bacteria that live in watery settings (such as Vibrio or Aeromonas).
Similarly, severe infections associated with intravenous drug use may be due to contamination of the injected substances.
In the past, gas gangrene was a common complication of battlefield injury, as wounds were often contaminated with dirt and there were delays to surgical treatment and access to antibiotics, if these were available at all.
How is it recognised?
Unfortunately, early necrotising fasciitis is easily missed. This is because the symptoms – fever, pain, swelling and tenderness at the affected site – may be non-specific or confused with a mild, superficial infection.
The hallmark of necrotising fasciitis is pain far more severe than expected for what might otherwise look like a minor infection. As the infection progresses, the skin becomes tense and discoloured, and patients may become severely unwell with low blood pressure and confusion.
Note also the author's response to the comment about the possibility of a spider bite causing this disease"
"...even quite minor trauma can allow bacteria in to cause infection. For many simple skin infections, athlete’s foot (a common fungal infection) is a common portal of entry."