Saturday, December 03, 2005
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 systemic inflammatory response syndrome (SIRS). Similar terms are sepsis syndrome, septic shock, and multiple organ dysfunction syndrome.
Bacteremia is an invasion of the bloodstream by bacteria.
Bacteremia occurs when bacteria enter the bloodstream. This may occur through a wound or infection, or through a surgical procedure or injection. Bacteremia may cause no symptoms and resolve without treatment, or it may produce fever and other symptoms of infection. In some cases, bacteremia leads to septic shock, a potentially life-threatening condition.
Causes and symptoms
Several types of bacteria live on the surface of the skin or colonize the moist linings of the urinary tract, lower digestive tract, and other internal surfaces. These bacteria are normally harmless as long as they are kept in check by the body's natural barriers and the immune system. People in good health with strong immune systems rarely develop bacteremia.
However, when bacteria are introduced directly into the circulatory system, especially in a person who is ill or undergoing aggressive medical treatment, the immune system may not be able to cope with the invasion, and symptoms of bacteremia may develop. For this reason, bacteremia is most common in people who are already affected by or being treated for some other medical problem. In addition, medical treatment may bring a person in contact with new types of bacteria that are more invasive than those already residing in that person's body, further increasing the likelihood of bacterial infection.
Conditions which increase the chances of developing bacteremia include:
immune suppression, either due to HIV infection or drug therapy
antibiotic therapy which changes the balance of bacterial types in the body
prolonged or severe illness
alcoholism or other drug abuse
diseases or drug therapy that cause ulcers in the intestines, e.g. chemotherapy for cancer
Common immediate causes of bacteremia include:
drainage of an abscess, including an abscessed tooth
urinary tract infection, especially in the presence of a bladder catheter
decubitus ulcers (pressure sores)
intravenous procedures using unsterilized needles, including IV drug use
prolonged IV needle placement
use of ostomy tubes, including gastrostomy (surgically making a new opening into the stomach), jejunostomy (surgically making an opening from the abdominal wall into the jejunum), and colostomy (surgically creating an articifical opening into the colon).
The bacteria most likely to cause bacteremia include members of the Staphylococcus, Streptococcus, Pseudomonas, Haemophilus, and Esherichia coli (E. coli) genera.
Symptoms of bacteremia may include:
fever over 101°F (38.3°C)
shortness of breath
Not all of these symptoms are usually present. In the elderly, confusion may be the only prominent symptom. Bacteremia may lead to septic shock, whose symptoms include decreased consciousness, rapid heart and breathing rates and multiple organ failures.
Bacteremia is diagnosed by culturing the blood for bacteria. Samples may need to be tested several times over several hours. Blood analysis may also reveal an elevated number of white blood cells. Blood pressure is monitored closely; a decline in blood pressure may indicate the onset of septic shock.
Antibiotics are the mainstay of treatment, and are often begun before positive identification of the bacteria is made. Close observation is required to guard against septic shock. Since bacteremia is usually associated with an existing infection elsewhere in the body, finding and treating this infection is an important part of treatment.
Bacteremia may cause no symptoms, but may be discovered through a blood test for another condition. In this situation, it may not need to be treated, except in patients especially at risk for infection, such as those with heart valve defects or whose immune systems are suppressed.
Prompt antibiotic therapy usually succeeds in clearing bacteria from the bloodstream. Recurrence may indicate an undiscovered site of infection. Untreated bacteria in the blood may spread, causing infection of the heart (endocarditis or pericarditis) or infection of the covering of the central nervous system (meningitis).
Bacteremia can be prevented by preventing the infections which often precede it. Good personal hygiene, especially during viral illness, may reduce the risk of developing bacterial infection. Treating bacterial infections quickly and thoroughly can minimize the risk of spreading infection. During medical procedures, the burden falls on medical professionals to minimize the number and duration of invasive procedures, to reduce patients' exposure to sources of bacteria when being treated, and to use scrupulous technique.
Surgical creation of an artificial anus on the abdominal wall by cutting into the colon and bringing it up to the surface.
Surgical creation of an artificial opening into the stomach through the abdominal wall to allow tube feeding.
Surgical creation of an opening to the middle portion of the small intestine (jejunum), through the abdominal wall.
A life-threatening drop in blood pressure caused by bacterial infection.
For Your Information
Harrison's Principles of Internal Medicine. Ed. Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.
The Meck Page. 13 Apr. 1998 http://www.merck.com
Source: Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group
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