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Bacteremic is a term that refers to the ability of a bacterium to multiply and cause an infection in the bloodstream. The invasion of the bloodstream by the particular type of bacteria is also referred to as bacteremia.

If the invading bacteria also release toxins into the bloodstream, the malady can also be called blood poisoning or septicemia. Staphylococcus and Streptococcus are typically associated with septicemia.

The bloodstream is susceptible to invasion by bacteria that gain entry via a wound or abrasion in the protective skin overlay of the body, or as a result of another infection elsewhere in the body, or following the introduction of bacteria during a surgical procedure or via a needle during injection of a drug.

Depending on the identity of the infecting bacterium and on the physical state of the human host (primarily with respect to the efficiency of the immune system ), bacteremic infections may not produce any symptoms. However, some infections do produce symptoms, ranging from an elevated temperature, as the immune system copes with the infection, to a spread of the infection to the heart (endocarditis or pericarditis) or the covering of nerve cells (meningitis ). In more rare instances, a bacteremic infection can produce a condition known as septic shock. The latter occurs when the infection overwhelms the ability of the body's defense mechanisms to cope. Septic shock can be lethal.

Septicemic infections usually result from the spread of an established infection. Bacteremic (and septicemic) infections often arise from bacteria that are normal resident on the surface of the skin or internal surfaces, such as the intestinal tract epithelial cells. In their normal environments the bacteria are harmless and even can be beneficial. However, if they gain entry to other parts of the body, these so-called commensal bacteria can pose a health threat. The entry of these commensal bacteria into the bloodstream is a normal occurrence for most people. In the majority of people, however, the immune system is more than able to deal with the invaders. If the immune system is not functioning efficiently then the invading bacteria may be able to multiply and establish an infection. Examples of conditions that compromise the immune system are another illness (such as acquired immunodeficiency syndrome and certain types of cancer), certain medical treatments such as irradiation, and the abuse of drugs or alcohol.

Examples of bacteria that are most commonly associated with bacteremic infections are Staphylococcus, Streptococcus, Pseudomonas, Haemophilus, and Escherichia coli .

The generalized location of bacteremia produces generalized symptoms. These symptoms can include a fever, chills, pain in the abdomen, nausea with vomiting, and a general feeling of ill health. Not all these symptoms are present at the same time. The nonspecific nature of the symptoms may not prompt a physician to suspect bacteremia until the infection is more firmly established. Septic shock produces more drastic symptoms, including elevated rates of breathing and heartbeat, loss of consciousness and failure of organs throughout the body. The onset of septic shock can be rapid, so prompt medical attention is critical.

The discovery of bacteria in the blood should be taken as grounds to suspect bacteremia, because bacteria do not typically populate blood. Antibiotic therapy is usually initiated immediately, even if other options, such as the transient entry of bacteria from a cut, have actually occurred. In addition, antibiotic therapy is prudent because many bacteremic infections arise because of an ongoing infection elsewhere in the body. Along with the prompt start of treatment, the antibiotic used must be selected with care. Use of an ineffective antibiotic can provide the bacteria with enough time to undergo explosive increases in number, whereas the use of an antibiotic to which the bacteria are susceptible can quickly quell a brewing infection.

As with many other infections, bacteremic infections can be prevented by observance of proper hygienic procedures including hand washing, cleaning of wounds, and cleaning sites of injections to temporarily free the surface of living bacteria. The rate of bacteremic infections due to surgery is much less now than in the past, due to the advent of sterile surgical procedures, but is still a serious concern.

See also Bacteria and bacterial infection; Infection and resistance