Қан ағымы инфекциясы және бактериемия

Bacterial or fungal infection of blood
the systemic immune response to bacterial infection in the blood

Bloodstream infections (BSIs) are infections of blood caused by blood borne pathogens. The detection of microbes in the blood (most commonly accomplished by blood cultures) is always abnormal. A bloodstream infection is different from sepsis, which is characterized by severe inflammatory or immune responses of the host organism to pathogens. 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. Immune responses to the bacteria can cause sepsis and septic shock, which have high mortality rates. Bacteria can also spread via the blood 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.

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 routes of entry into the bloodstream that lead to bacteremia. Causes of bacteremia can additionally be divided into healthcare associated (acquired during the process of receiving care in a healthcare facility) or community acquired (acquired outside of a health facility, often prior to hospitalization).

Gram positive bacteria are an increasingly important cause of bacteremia. Staphylococcus, 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. Staphylococcus aureus is the most common cause of healthcare 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 healthcare 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. Enterococci are an important cause of healthcare 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 enterococcal species can cause bacteremia in patients who have had long hospital stays or frequent antibiotic use in the past (see antibiotic misuse).

Bacteremia can travel through the blood stream to distant sites in the body and cause infection (hematogenous spread). Hematogenous spread of bacteria is part of the pathophysiology of certain infections of the heart (endocarditis), structures around the brain (meningitis), and tuberculosis of the spine (Pott's disease). Hematogenous spread of bacteria is responsible for many bone infections (osteomyelitis). Prosthetic cardiac implants (for example artificial heart valves) are especially vulnerable to infection from bacteremia. Prior to widespread use of vaccines, occult bacteremia was an important consideration in febrile children that appeared otherwise well.

Bacteremia is most commonly diagnosed by blood culture, in which a sample of blood drawn from the vein by needle puncture is allowed to incubate with a medium that promotes bacterial growth. If 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 example, if the skin is not adequately cleaned before needle puncture, contamination of the blood sample with normal bacteria that live on the surface of the skin can occur. For this reason, blood cultures must be drawn with great attention to sterile process. The presence of certain bacteria in the blood culture, such as Staphylococcus aureus, Streptococcus pneumoniae, and Escherichia coli almost never represent a contamination of the sample. On the other hand, contamination may be more highly suspected if organisms like Staphylococcus epidermidis or Cutibacterium acnes grow in the blood culture. Two blood cultures drawn from separate sites of the body are often sufficient to diagnose bacteremia.

Bacteremia is the presence of bacteria in the bloodstream that are alive and capable of reproducing. It is a type of bloodstream infection. Bacteremia is defined as either a primary or secondary process. In primary bacteremia, bacteria have been directly introduced into the bloodstream. Injection drug use may lead to primary bacteremia. In the hospital setting, use of blood vessel catheters contaminated with bacteria may also lead to primary bacteremia. Bacteria that have infected the body at these sites may then spread into the lymphatic system and gain access to the bloodstream, where further spread can occur. Bacteremia may also be defined by the timing of bacteria presence in the bloodstream: transient, intermittent, or persistent. In transient bacteremia, bacteria are present in the bloodstream for minutes to a few hours before being cleared from the body, and the result is typically harmless in healthy people. This can occur after manipulation of parts of the body normally colonized by bacteria, such as the mucosal surfaces of the mouth during tooth brushing, flossing, or dental procedures, or instrumentation of the bladder or colon.

The presence of bacteria in the blood almost always requires treatment with antibiotics. This is because there are high mortality rates from progression to sepsis if antibiotics are delayed. Empiric antibiotics should be narrowed, preferably to a single antibiotic, once the blood culture returns with a particular bacteria that has been isolated. Uncomplicated bacteremia is defined as having positive blood cultures for MRSA, but having no evidence of endocarditis, no implanted prostheses, negative blood cultures after 2–4 days of treatment, and signs of clinical improvement after 72 hrs. In particular, a recent history of exposure to a healthcare setting may necessitate the need for antibiotics with pseudomonas aeruginosa coverage or broader coverage for resistant organisms. Long term catheters (>14 days) should be removed if the patient is developing signs or symptoms of sepsis or endocarditis, or if blood cultures remain positive for more than 72 hours.