the presence of bacteria in the bloodstream, whether associated with active disease or not. The transient bacteremia that follows dental manipulation or surgical (surgery) procedures may have little significance in the otherwise healthy individual with a functioning immune system. By contrast, extensive bacteremia, when it is associated with the release of bacterial toxins into the circulation (septicemia), can be a serious medical emergency leading to bacteremic shock and eventual vascular collapse. Even transient bacteremia can be a serious matter for those with prosthetic devices (which can serve as foci for infection) or for those with debilitating medical conditions that increase susceptibility to bacterial invasion.

Bacteremia usually follows infection of a primary site or is associated with particularly high-risk surgical procedures, particularly in the digestive or urinary tract, that release bacteria from sequestered sites into the blood, which may carry infection to remote parts of the body. Bacteremia can often be anticipated in those undergoing high-risk surgical procedures, with preventive antibiotic therapy being given to forestall extensive bacterial invasion of the bloodstream. Despite such precautions, the development of antibiotic-resistant strains of bacteria (e.g., methicillin-resistant Staphylococcus aureus, or MRSA) has led to an increase in the incidence of severe bacteremia since the late 1960s.