1. A morbid condition of the blood, characterized by the presence and possible multiplication of pathogenic bacteria entering from a region of infection; such as, an infected wound: Septicemia is marked by chills, fever, prostration, and degenerative and inflammatory changes in the internal organs.
2. A systemic disease caused by pathogenic organisms or their toxins in the bloodstream: Also known as blood poisoning, septicemia is a condition that is caused by the spread of germs and their infective elements via the circulating blood.

Bacteria often commonly enter the bloodstream (a condition called "bacteremia" or blood poisoning), but usually only a small number of bacteria do this and so no symptoms develop of septicemia.

Most bacteria that enter the bloodstream are rapidly removed by white blood cells. Sometimes there are too many bacteria to be removed easily, and septicemia can develop.

A sickness that is widespread throughout the bloodstream is called "sepsis", or septicemia, which can cause severe symptoms of illness.