Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link



Joseph D Forrester

, MD, MSc, Stanford University

Reviewed/Revised Mar 2023 | Modified Sep 2023
Topic Resources

Bacteremia is the presence of bacteria in the bloodstream.

Usually, bacteremia, particularly if it occurs during ordinary activities, does not cause infections because bacteria typically are present only in small numbers and are rapidly removed from the bloodstream by the immune system. However, if bacteria are present long enough and in large enough numbers, particularly in people who have a weakened immune system, bacteremia can lead to other infections and sometimes trigger a serious bodywide response called sepsis Sepsis and Septic Shock Sepsis is a serious bodywide response to bacteremia or another infection plus malfunction or failure of an essential system in the body. Septic shock is life-threatening low blood pressure ... read more .

Bacteria that are not removed by the immune system may accumulate in various places throughout the body, causing infections there, as in the following:

In bacteremia, bacteria tend to lodge and collect on certain body structures, such as abnormal heart valves. Bacteria are particularly likely to collect on any artificial material present in the body, such as intravenous catheters and artificial (prosthetic) joints and heart valves. These collections (colonies) of bacteria may remain attached to the sites and continuously or periodically release bacteria into the bloodstream.

Causes of Bacteremia

Bacteremia may occur during

  • Certain ordinary activities

  • Dental or medical procedures

  • Certain bacterial infections

  • Injection of illicit drugs

Ordinary activities sometimes cause bacteremia in healthy people. For example, vigorous toothbrushing can cause bacteremia because bacteria living on the gums around the teeth are forced into the bloodstream. Bacteria may also enter the bloodstream from the intestine during digestion. Bacteremia that occurs during ordinary activities rarely leads to infections.

Dental or medical procedures can lead to bacteremia. During dental procedures (as during tooth cleaning by a dental hygienist), bacteria living on the gums may become dislodged and enter the bloodstream. Bacteremia may also occur when catheters are inserted into the bladder or tubes are inserted into the digestive tract or urinary tract. Bacteria may be present in the area where the catheter or tube has been inserted (such as the bladder or intestine). So even though sterile techniques are used, these procedures may move bacteria into the bloodstream. Surgical treatment of infected wounds, abscesses (collections of pus), and pressure sores can dislodge bacteria from the infected site, causing bacteremia.

Injecting illicit drugs can cause bacteremia because the needles used are usually contaminated with bacteria, and people may not properly cleanse their skin.

Symptoms of Bacteremia

Usually, bacteremia that results from ordinary events, such as dental procedures, is temporary and causes no symptoms. Bacteremia that results from other conditions may cause fever. If people with bacteremia have fever, a rapid heart rate, shaking chills, low blood pressure, gastrointestinal symptoms (such as abdominal pain, nausea, vomiting, and diarrhea), rapid breathing, and/or become confused, they probably have sepsis or septic shock Sepsis and Septic Shock Sepsis is a serious bodywide response to bacteremia or another infection plus malfunction or failure of an essential system in the body. Septic shock is life-threatening low blood pressure ... read more .

Diagnosis of Bacteremia

  • Culture of a blood sample

If bacteremia, sepsis, or septic shock is suspected, doctors usually take a sample of blood so they can try to grow (culture Culture of Microorganisms Infectious diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites. Doctors suspect an infection based on the person's symptoms, physical examination results,... read more ) the bacteria in the laboratory and identify it. If needed, doctors may try to culture bacteria from other samples (such as urine or sputum).

Treatment of Bacteremia

  • Antibiotics

If an infection or sepsis develops, it is treated with antibiotics.

Doctors remove sources of bacteria (such as catheters).

Prevention of Bacteremia

People who are at high risk of complications due to bacteremia (such as those who have an artificial heart valve or joint or certain heart valve abnormalities) are often given antibiotics before procedures that can cause bacteremia:

  • Dental procedures

  • Surgical treatment of infected wounds

Antibiotics help prevent bacteremia and thus infections and sepsis from developing.

quiz link

Test your knowledge

Take a Quiz!