Bacteremia describes the presence of bacteria in the blood. It always suggests a pathology as blood is normally free of bacteria.
Bacteria can enter the bloodstream in several ways, but the most serious cause is a complication of an infection that affects another part of the body which spreads. It can also be caused by surgery or dental work. In a hospital environment, it can be the result of improper sterilization of a catheter or intravenous line. In drug addicts, it can be caused by a non-sterile hypodermic needle.