Bacteremia

Bacteremia (Bacteræmia in British English) is the presence of bacteria in the blood. The blood is normally a sterile environment, so the detection of bacteria in the blood (most commonly with blood cultures) is always abnormal.

Bacteria can enter the bloodstream as a severe complication of infections (like pneumonia or meningitis), during surgery (especially when involving mucous membranes such as the gastrointestinal tract), or due to catheters and other foreign bodies entering the arteries or veins (including intravenous drug abuse).

Bacteremia can have several consequences. The immune response to the bacteria can cause sepsis (blood poisoning) and septic shock, which has a relatively high mortality rate. Bacteria can also use the blood to spread to other parts of the body (which is called hematogenous spread), causing infections away from the original site of infection. Examples include endocarditis or osteomyelitis. Treatment is with antibiotics, and prevention with antibiotic profylaxis can be given in situations where problems are to be expected.

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Definition

Bacteremia is different to sepsis (so-called blood poisoning or toxemia), which is a condition where bacteremia is associated with an inflammatory response from the body (causing systemic inflammatory response syndrome, characterised by rapid breathing, low blood pressure, fever, etc.). For example, a dental procedure (or even brushing your teeth) introduces a detectable amount of bacteria into the bloodstream, but these are unable to replicate in the blood of most people. Some patients with prosthetic heath valves however need antibiotic cover for dental surgery because the bacteremia might lead to endocarditis (infection of the interior lining of the heart).

Septicemia is an ill-defined non-scientific term introducing more confusion between sepsis and bacteremia: it suggests that there is something the bloodstream causing sepsis.

Diagnosis

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 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.

Causes

In the hospital, indwelling catheters are a frequent cause of bacteremia and 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, intravenous drug use, and colorectal cancer. Bacteremia may also be seen in oropharyngeal, gastrointestinal or genitourinary surgery or exploration.

Consequences

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 septic shock, and may result in multiple organ dysfunction syndrome.

Bacteremia is the principal means by which local infections are 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. Hematogenous dissemination of bacteria is part of the pathophysiology of meningitis and endocarditis, and of Pott's disease and many other forms of osteomyelitis.

See also

• Antibiotic prophylaxis
• Fungemia
• Sepsis
• Viremia