Cuts or grazes to the skin may be a source, but such damage may be trivial or may go unnoticed. Sometimes it may occur in hospitalised patients after surgery. When it arises in the community, the source is usually the patient s own Strep pyogenes strain. This has yet to be proved. Other risk factors include diabetes, age over 50 years, steroid treatment, high blood pressure, obesity and alcoholism.
Excessive pain is an early warning symptom.
Bacteria spreads very rapidly in the tissues below the skin surface, well ahead of any visible changes in the overlying skin. Infection may progress at inches per hour, the patient rapidly becomes generally unwell, with progressive deterioration out of all proportion to the visible changes in the skin of the affected area. By this stage, infection may have penetrated deep into the underlying tissues. Patients often develop shock, with collapse, low blood pressure, and failure of liver, kidneys and other vital systems. The key to patient survival is swift recognition and immediate treatment.