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Bacteremia (also bacteraemia) is the presence of bacteria in the blood. Blood is normally a sterile environment, so the detection of bacteria in the blood (most commonly accomplished by blood cultures) is always abnormal. It is distinct from sepsis, which is the host response to the bacteria.
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 during intravenous drug abuse). Transient bacteremia can result after dental procedures or brushing of teeth.
Bacteremia can have several important health consequences. The immune response to the bacteria can cause sepsis 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, such as endocarditis or osteomyelitis. Treatment for bacteremia is with antibiotics, and prevention with antibiotic prophylaxis can be given in high risk situations.
Bacteremia is the presence of bacteria in the blood stream that are alive and capable of reproducing. It is a type of bloodstream infection. Bacteremia is clinically distinct from sepsis, which is a condition where the blood stream infection is associated with an inflammatory response from the body (often causing systemic inflammatory response syndrome, characterised by rapid breathing, low blood pressure, fever, etc.). Common oral hygiene, such as brushing teeth or flossing, can cause transient but harmless bacteremia. Some patients with prosthetic heart valves however need antibiotic prophylaxis for dental surgery because bacteremia might lead to endocarditis (infection causing inflammation of the interior lining of the heart).
Bacteria can enter the bloodstream in a number of different ways. However, for each major classification of bacteria (gram negative, gram positive, or anaerobic) there are characteristic sources or mechanisms that lead to bacteremia. Causes of bacteremia can additionally be divided into community-acquired or health-care associated.
Gram positive bacteria are an increasingly important cause of bacteremia. Staphyloccocus, streptococcus, and enterococcus species are the most important and most common species of gram-positive bacteria that can enter the bloodstream. These bacteria are normally found on the skin or in the gastrointestinal tract.
Staph aureus is the most common cause of health care associated bacteremia in North and South America and is also an important cause of community-acquired bacteremia. Skin ulceration or wounds, respiratory tract infections, and IV drug use are the most important causes of community-acquired staph aureus bacteremia. In health care settings, intravenous catheters, urinary tract catheters, and surgical procedures are the most common causes of staph aureus bacteremia.
There are many different types of streptococcal species that can cause bacteremia. Group A streptococcus (GAS) typically causes bacteremia from skin and soft tissue infections. Group B streptococcus is an important cause of bacteremia in neonates, often immediately following birth. Viridans streptococci species are normal bacterial flora of the mouth. Viridans strep can cause temporary bacteremia after eating, toothbrushing, or flossing. More severe bacteremia can occur following dental procedures or in patients receiving chemotherapy. Finally, streptococcus bovis is a common cause of bacteremia in patients with colon cancer.
Enterococci are an important cause of health-care associated bacteremia. These bacteria commonly live in the gastrointestinal tract and female genital tract. Intravenous catheters, urinary tract infections and surgical wounds are all risk factors for developing bacteremia from enterococcal species. Resistant enterococci species can cause bacteremia in patients who have had long hospital stays or frequent antibiotic use in the past.
Bacteremia may also be seen in oropharyngeal, gastrointestinal or genitourinary surgery or exploration. Salmonella infection, despite mainly only resulting in gastroenteritis in the developed world, is a common cause of bacteremia in Africa. It principally affects children who lack antibodies to Salmonella and HIV+ patients of all ages.
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.
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.
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