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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
  • malnutrition
  • 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)
  • chills
  • malaise
  • abdominal pain
  • nausea
  • vomiting
  • diarrhea
  • anxiety
  • shortness of breath
  • confusion
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.


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.

Key terms

Colostomy — Surgical creation of an artificial anus on the abdominal wall by cutting into the colon and bringing it up to the surface.
Gastrostomy — Surgical creation of an artificial opening into the stomach through the abdominal wall to allow tube feeding.
Jejunostomy — Surgical creation of an opening to the middle portion of the small intestine (jejunum), through the abdominal wall.
Septic shock — A life-threatening drop in blood pressure caused by bacterial infection.



The Merck Page. April 13, 1998.


the presence of bacteria in the blood. (See accompanying table.)


The presence of viable bacteria in the circulating blood; may be transient following trauma such as dental or other iatrogenic manipulation or may be persistent or recurrent as a result of infection.
Synonym(s): bacteriemia
[bacteria + G. haima, blood]


/bac·ter·e·mia/ (-e´me-ah) the presence of bacteria in the blood.


The presence of bacteria in the blood.

bac′te·re′mic (-mĭk) adj.
bac′te·re′mi·cal·ly adv.


Etymology: Gk, bakterion, small staff, haima, blood
the presence of bacteria in the blood. Undocumented bacteremias occur frequently and usually abate spontaneously. Bacteremia is demonstrated by blood culture. Antibiotic treatment, if given, is specific for the organism found and appropriate to the locus of infection. If untreated, bacteremia can be fatal. Also spelled bacteraemia,bacteriemia. Compare septicemia. See also septic shock. bacteremic, adj.


The presence of bacteria in blood


The presence of viable bacteria in the circulating blood; may be transient following trauma such as dental or other iatrogenic manipulation or may be persistent or recurrent as a result of infection.
Synonym(s): bacteriemia, bacteraemia.
[bacteria + G. haima, blood]

bacteremia (bak·t·rēˑ·mē·),

n condition marked by the presence of bacteria in the bloodstream.


Presence of viable bacteria in circulating blood; may be transient following trauma such as dental or other iatrogenic manipulation or may be persistent or recurrent as a result of infection.
Synonym(s): bacteraemia.
[bacteria + G. haima, blood]

bacteremia (bak´tirē´mēə),

n 1. the presence of bacteria in the bloodstream. It may be transient, intermittent, or continuous. Transient bacteremia may result from dental procedures such as extraction and adult prophylaxis or it may accompany the early phases of many infections. Continuous bacteremia is a feature of endocarditis.
n 2. the presence of bacteria in the blood (e.g., as occurs during adult prophylaxis of a patient with the risk of complications due to bacteremia).


the temporary presence of bacteria in the blood. The condition is not manifested by any clinical signs but is commonly followed by the development of embolic infections such as arthritis, meningitis, endocarditis, and liver and lung abscesses.
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