What causes septicaemia to occur?

Bloodstream . In some cases untreated bacterial infection can spread to the circulatory system and result in septicemia.
Infection. Septicemia, or sepsis, is a total body reaction to infection. There are specific criteria - such as fever, high white cells (which are infection fighting cells), fast heart rate, and fast breathing - that, when coupled with infection, is called sepsis. Sometimes, the reaction can be so severe it can cause shock, a scarring reaction in the lungs or even liver and kidney damage.