Blood poisoning, also known as septicaemia, is a bacterial infection that occurs when bacteria get into the bloodstream and multiply rapidly. Blood poisoning normally happens when bacteria enter the bloodstream in large numbers, and spread too quickly for the immune system to destroy them. Once in the bloodstream, some types of bacteria release poisons known as toxins that attack the body’s tissues. Blood poisoning is a potentially life-threatening infection that must be treated rapidly in order to prevent the infection from spreading to the heart and lungs.