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Bacteremia (Bacteræmia in British English) is the presence of bacteria in the blood. It is the principal means by which local infections spread to distant organs (referred to as hematogenous spread). Bacteremia is typically transient rather than continuous, due to a vigorous immune system response when bacteria are detected in the blood. Bacteremia is commonly referred to as "blood poisoning".
Bacteremia is most commonly diagnosed by blood culture, in which a sample of blood is allowed to incubate with a medium that promotes bacterial growth. Since blood is normally sterile, this process does not normally lead to the isolation of bacteria. If, however, bacteria are present in the bloodstream at the time the sample is obtained, the bacteria will multiply in the medium and can thereby be detected. Any bacteria that incidentally find their way to the culture medium will also multiply. For this reason, blood cultures must be drawn with great attention to sterile process. Occasionally, blood cultures will reveal the presence of bacteria that represent contamination from the skin through which the culture was obtained. Blood cultures must be repeated at intervals to determine if persistent—rather than transient—bacteremia is present.
Hematogenous dissemination of bacteria is part of the pathophysiology of meningitis and endocarditis, and of Pott's disease and many other forms of osteomyelitis. In the hospital, indwelling catheters are a frequent cause of bacteremia and the subsequent nosocomial infections, because they provide a means by which bacteria normally found on the skin can enter the bloodstream. Other causes of bacteremia include dental procedures (occasionally including simple tooth brushing), herpes (including herpetic whitlow), urinary tract infections, IV drug use, and colorectal cancer. Bacteremia may also be seen in oropharyngeal, gastrointestinal or genitourinary surgery or exploration.
A related condition, septicemia, refers to the presence of bacteria or their toxins in the bloodstream.
Bacteremia, as noted above, frequently elicits a vigorous immune system response. The constellation of findings related to this response (such as fever, chills, or hypotension) is referred to as sepsis. In the setting of more severe disturbances of temperature, respiration, heart rate or white blood cell count, the response is characterized as sepsis syndrome, septic shock, and may result in multiple organ dysfunction syndrome.
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