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Bacteremia refers to the presence of bacteria in the blood.
The presence of bacteria in the bloodstream assumes they are alive and capable of reproducing.
Bacteremia is a type of bloodstream infection.
Blood is normally a sterile environment.
The detection of bacteria in the blood is always abnormal.
It is defined as either a primary or secondary process.
In primary bacteremia, bacteria have been directly introduced into the bloodstream.
Sepsis, refers to a host response to the bacteria, and is distinct from bacteremia.
With sepsis the blood stream infection is associated with an inflammatory response from the body, often causing abnormalities in body temperature, heart rate, breathing rate, blood pressure, and white blood cell count.
Bacteria can enter the bloodstream as a severe complication of infections, during surgery, or due to catheters and other foreign bodies entering the arteries or veins, including during intravenous drug abuse.
A transient bacteremia can result after dental procedures or brushing of teeth.
Bacteremia health consequences: immune response to the bacteria can cause sepsis and septic shock; hematogenous spread, causing infections away from the original site of infection, such as endocarditis or osteomyelitis.
Bacteremia is typically transient and is quickly removed from the blood by the immune system.
It frequently evokes an immune system response called Sepsis.
Sepsis consists of symptoms such as fever, chills, and hypotension.
Severe immune responses to bacteremia may result in septic shock and multiple organ dysfunction syndrome.
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.
Bacteremia can be divided into healthcare-associated or community-acquired
Gram positive bacteremia-Staphylococcus, streptococcus, and enterococcus species are the most important and most common species of gram-positive bacteria that can enter the bloodstream.
Gram positive bacteria are normally found on the skin or in the gastrointestinal tract.
The most common cause of healthcare-associated bacteremia in North and South America is and is Staphylococcus aureus.
Staphylococcus aureus is also an important cause of community-acquired bacteremia.
Community-acquired staph aureus bacteremia are commonly associated with skin ulceration or wounds, respiratory tract infections, and IV drug use.
In healthcare settings Staph aureus bacteremia commonly associated with intravenous catheters, urinary tract catheters, and surgical procedures.
A number of different types of streptococcal species that can cause bacteremia.
Group A streptococcus 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 are normal bacterial flora of the mouth, and can cause temporary bacteremia after eating, toothbrushing, or flossing.
Streptococcus bovis is a common cause of bacteremia in patients with colon cancer.
Enterococci bacteria commonly live in the gastrointestinal tract and female genital tract.
Enterococci bacteremia are associated with intravenous catheters, urinary tract infections and surgical wounds.
Resistant enterococcal bacteremia occurs in patients who have had long hospital stays or frequent antibiotic use in the past.
Gram negative bacteria are responsible for approximately 24% of all cases of healthcare-associated bacteremia and 45% of all cases of community-acquired bacteremia.
Generally, gram negative bacteria enter the bloodstream from the respiratory tract, genitourinary tract, gastrointestinal tract, or hepatobiliary systems.
Gram-negative bacteremia occurs more frequently in elderly.
Graham-negative bacteremia is associated with the higher degree of morbidity and mortality in the elderly.
E.coli infection is the most common cause of community-acquired bacteremia.
E. coli bacteremia accounts for 75% of cases in the community, and is usually the result of a urinary tract infection.
Other gram- negative organisms that can cause community-acquired bacteremia include: Pseudomonas aeruginosa, Klebsiella pneumoniae, and Proteus mirabilis.
Gram negative organisms are an important cause of bacteremia in ICU associated healthcare-associated cases: Pseudomonas and Enterobacter species are the most important causes of gram negative bacteremia in the ICU.
Gram negative bacteria enter the bloodstream via catheters in veins, arteries, or urinary tract.
Surgery on the genitourinary tract, intestinal tract, or hepatobiliary tract can lead to gram negative bacteremia.
Bacteremia risk factors include:
HIV infection
Diabetes Mellitus
Chronic hemodialysis
Solid organ transplant
Stem cell transplant
Treatment with glucocorticoids
Liver failure
Asplenia
Bacteremia can lead to infections: endocarditis, meningitis, and osteomyelitis.
It is most commonly diagnosed by blood culture.
If the skin is not adequately cleaned before needle puncture, contamination with normal bacteria that live on the surface of the skin can occur.
The presence of certain bacteria, as Staphylococcus aureus, Streptococcus pneumoniae, and Escherichia coli almost never represent a contamination.
Contamination of the blood specimen may be more highly suspected if organisms like Staphylococcus epidermidis or C. acnes grow in the blood culture.
Two blood cultures drawn from separate sites of the body are often sufficient to diagnose bacteremia.
Two out of two cultures growing the same type of bacteria usually represents a real bacteremia.
One out of two positive cultures will usually prompt a repeat set of blood cultures to be drawn to confirm whether a contaminant or a real bacteremia is present.
Blood cultures may be repeated at intervals to determine if persistent or rather than transient bacteremia is present.
In patients with bacteremia due to Staphylococcus aureus echocardiogram of the heart is recommended to rule out infectious endocarditis.
Primary bacteremia may result from IV drug injection, from blood vessel catheters contaminated with bacteria
Secondary bacteremia occurs when bacteria have entered the body at other sites: skin, or the mucous membranes of the lungs, mouth or gastrointestinal tract, urinary tract or genitals.
Bacteria at these sites may then spread into the lymphatic system and gain access to the bloodstream.
Bacteremia may characterized as transient, intermittent, or persistent.
In transient bacteremia, bacteria are present in the bloodstream for minutes to a few hours before being cleared.
Transient bacteremia is typically harmless in healthy people.
Transient bacteremia occurs after manipulation of the body tissues normally colonized by bacteria, such as the mucosal surfaces of the mouth.
This occurs during teeth brushing, flossing, or dental procedures.
Transient bacteremia also occurs with instrumentation of the bladder or colon.
Intermittent bacteremia occurs due to periodic seeding of the same bacteria into the bloodstream by an existing infection elsewhere in the body,.
Sources of intermittent bacteremia include: abscess, pneumonia, and bone infection.
With intermittent bacteremia clearing of that bacteria from the bloodstream occurs.
Persistent bacteremia manifests by the continuous presence of bacteria in the bloodstream.
Persistent bacteremia usually results from an infected heart valve, a central line-associated bloodstream infection, an infected blood clot, or an infected blood vessel graft.
A persistent bacteremia can also occur as part of the infection process: typhoid fever, brucellosis, and bacterial meningitis.
Persistent bacteremia can be potentially fatal.
Treatment
Bacteria almost always requires treatment with antibiotics, as there is a high mortality rates from progression to sepsis if antibiotics are delayed.
Bacteremia is treated empirically with intravenous antibiotic coverage.
The choice of antibiotic is determined by the most likely source of infection and the characteristic organisms that typically cause that infection.
Empiric antibiotics should be narrowed, preferably to a single antibiotic.
Gram positive methicillin resistant staph aureus (MRSA) bacteremia should be treated with a 14-day course of intravenous vancomycin.
Uncomplicated bacteremia is defined as having positive blood cultures for MRSA, with no evidence of endocarditis, no implanted prostheses in place, negative blood cultures after 2–4 days of treatment, and signs of clinical improvement after 72 hrs.
Gram negative bacteremia treatment of gram negative bacteremia is also highly dependent on the causative organism.
Empiric antibiotic is guided by the most likely source of infection and prior exposure to healthcare facilities with risk of resistant organisms.
Cephalosporins such as ceftriaxone or beta lactam/beta lactam inhibitor antibiotics such as piperacillin-tazobactam are frequently used for the treatment of gram negative bacteremia.
For healthcare-associated bacteremia due to intravenous catheters guidelines for catheter removal: Short term catheters in place <14 days should be removed if bacteremia is caused by any gram negative bacteria, staph aureus, enterococci or mycobacteria.
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.
Fever is absent is up to 30% of all the people with bacteremia, and this absence is associated with poor outcome.