| Bloodstream infections | |
|---|---|
| Other names | Blood infection, toxemia, bacteremia, septicemia |
| Specialty | Infectious diseases  |
Bloodstream infections (BSIs) are infections ofblood caused byblood-borne pathogens.[1] The detection ofmicrobes in the blood (most commonly accomplished byblood cultures[2]) is always abnormal. A bloodstream infection is different fromsepsis, which is characterized by severeinflammatory orimmune responses of the host organism to pathogens.[3]
Bacteria can enter the bloodstream as a severe complication ofinfections (likepneumonia ormeningitis), during surgery (especially when involvingmucous membranes such as thegastrointestinal tract), or due tocatheters and otherforeign bodies entering thearteries orveins (including duringintravenousdrug abuse).[4] Transient bacteremia can result after dental procedures or brushing of teeth.[5]
Bacteremia can have several important health consequences. Immune responses to the bacteria can causesepsis andseptic shock, which, particularly if severe sepsis and then septic shock occurs, have highmortality rates, especially if not treated quickly (though, if treated early, currently mild sepsis can usually be dealt with successfully).[6] 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 asendocarditis orosteomyelitis.[citation needed] Treatment for bacteremia is withantibiotics, and prevention withantibiotic prophylaxis can be given in high risk situations.[7]
Bacteremia is typically transient and is quickly removed from the blood by theimmune system.[5]
Bacteremia frequently evokes a response from the immune system calledsepsis, which consists of symptoms such asfever, chills, andhypotension.[8] Severe immune responses to bacteremia may result inseptic shock andmultiple organ dysfunction syndrome,[8] which are potentially fatal.
Based on type of causative microbe, bloodstream infections are of many types:
| Type of blood-borne infection | Causative microbe | Description | Examples |
|---|---|---|---|
| Bacteremias | Bacteria | Bacteremia, in the strictest sense, refers to presence ofviable bacteria in the blood. Asymptomatic bacteremia can occur in normal daily activities such as conducting oral hygiene and after minor medical procedures. In a healthy person, these clinically benign infections are transient and cause no further sequelae. However, when immune response mechanisms fail or become overwhelmed, bacteremia becomes a bloodstream infection that can evolve into many clinical spectrums and is differentiated as septicemia.[9] |
|
| Viremias | Viruses | Viremia is a medical condition whereviruses enter thebloodstream and hence have access to the rest of the body. It is similar tobacteremia, a condition wherebacteria enter the bloodstream.[10] The name comes from combining the word "virus" with the Greek word for "blood" (haima). It usually lasts for 4 to 5 days in the primary condition. | |
| Fungemias | Fungi | Fungemia is the presence offungi oryeasts in theblood. The most common type, also known ascandidemia,candedemia, orsystemiccandidiasis, is caused byCandida species; candidemia is also among the most common bloodstream infections of any kind.[11] Infections by other fungi, includingSaccharomyces,Aspergillus (as in aspergillemia, also called invasiveaspergillosiis) andCryptococcus, are also called fungemia. It is most commonly seen inimmunosuppressed orimmunocompromisedpatients with severeneutropenia,cancer patients, or in patients with intravenouscatheters. | Candidemia, aspergillemia (invasiveaspergillosis) |
| Protozoemia (blood-borne protozoal infections) | Protozoa | Protozoan infections areparasitic diseases caused by organisms formerly classified in the kingdomProtozoa. These organisms are now classified in the supergroupsExcavata,Amoebozoa,Harosa (SAR supergroup), andArchaeplastida. They are usually contracted by either an insect vector or by contact with an infected substance or surface.[12] |
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 intohealthcare-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).[citation needed]
Gram positive bacteria are an increasingly important cause of bacteremia.[13] 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 thegastrointestinal tract.[citation needed]
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.[14] 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.[15]
There are many different types ofstreptococcal species that can cause bacteremia.Group A streptococcus (GAS) typically causes bacteremia from skin and soft tissue infections.[16]Group B streptococcus is an important cause of bacteremia inneonates, often immediately following birth.[17]Viridans streptococci species are normal bacterial flora of the mouth. Viridans strep can cause temporary bacteremia after eating, toothbrushing, or flossing.[17] More severe bacteremia can occur following dental procedures or in patients receiving chemotherapy.[17] Finally,Streptococcus bovis is a common cause of bacteremia in patients with colon cancer.[18]
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.[19]Resistant enterococcal species can cause bacteremia in patients who have had long hospital stays or frequent antibiotic use in the past (seeantibiotic misuse).[20]
Gram negative bacterial species are responsible for approximately 24% of all cases of healthcare-associated bacteremia and 45% of all cases of community-acquired bacteremia.[21][22] In general, gram negative bacteria enter the bloodstream from infections in therespiratory tract,genitourinary tract, gastrointestinal tract, orhepatobiliary system. Gram-negative bacteremia occurs more frequently in elderly populations (65 years or older) and is associated with highermorbidity and mortality in this population.[23]E.coli is the most common cause of community-acquired bacteremia accounting for approximately 75% of cases.[24] E.coli bacteremia is usually the result of a urinary tract infection. Other organisms that can cause community-acquired bacteremia includePseudomonas aeruginosa,Klebsiella pneumoniae, andProteus mirabilis.Salmonella infection, despite mainly only resulting in gastroenteritis in the developed world, is a common cause of bacteremia in Africa.[25] It principally affects children who lack antibodies to Salmonella and HIV+ patients of all ages.[26]
Among healthcare-associated cases of bacteremia, gram negative organisms are an important cause of bacteremia in theICU.[27] Catheters in the veins, arteries, or urinary tract can all create a way for gram negative bacteria to enter the bloodstream.[16] Surgical procedures of the genitourinary tract, intestinal tract, or hepatobiliary tract can also lead to gram negative bacteremia.[16]Pseudomonas andEnterobacter species are the most important causes of gram negative bacteremia in the ICU.[27]
There are several risk factors that increase the likelihood of developing bacteremia from any type of bacteria.[13][28] These include:
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).[30]
Prosthetic cardiac implants (for exampleartificial heart valves) are especially vulnerable to infection from bacteremia.[31] Prior to widespread use of vaccines, occult bacteremia was an important consideration in febrile children that appeared otherwise well.[32]
Bacteremia is most commonly diagnosed byblood culture, in which a sample of blood drawn from the vein by needle puncture is allowed toincubate with amedium that promotes bacterial growth.[33] If bacteria are present in the bloodstream at the time the sample is obtained, the bacteria will multiply and can thereby be detected.[citation needed]
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.[34] For this reason, blood cultures must be drawn with great attention to sterile process. The presence of certain bacteria in the blood culture, such asStaphylococcus aureus,Streptococcus pneumoniae, andEscherichia coli almost never represent a contamination of the sample. On the other hand, contamination may be more highly suspected if organisms likeStaphylococcus epidermidis orCutibacterium acnes grow in the blood culture.[citation needed]
Two blood cultures drawn from separate sites of the body are often sufficient to diagnose bacteremia.[34] Two out of two cultures growing the same type of bacteria usually represents a real bacteremia, particularly if the organism that grows is not a common contaminant.[34] 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.[34] The patient's skin is typically cleaned with an alcohol-based product prior to drawing blood to prevent contamination.[34] Blood cultures may be repeated at intervals to determine if persistent—rather than transient—bacteremia is present.[34]
Prior to drawing blood cultures, a thorough patient history should be taken with particular regard to presence of both fevers and chills, other focal signs of infection such asin the skin or soft tissue, a state of immunosuppression, or any recent invasive procedures.[33]
Ultrasound of the heart is recommended in all those with bacteremia due toStaphylococcus aureus to rule outinfectious endocarditis.[35]
Bacteremia is the presence ofbacteria in the bloodstream that are alive and capable of reproducing. It is a type of bloodstream infection.[36] Bacteremia is defined as either a primary or secondary process. In primary bacteremia, bacteria have been directly introduced into the bloodstream.[37]Injection drug use may lead to primary bacteremia. In the hospital setting, use of blood vesselcatheters contaminated with bacteria may also lead to primary bacteremia.[37] Secondary bacteremia occurs when bacteria have entered the body at another site, such as the cuts in the skin, orthe mucous membranes of the lungs (respiratory tract), mouth or intestines (gastrointestinal tract),bladder (urinary tract), or genitals.[38] Bacteria that have infected the body at these sites may then spread into thelymphatic system and gain access to the bloodstream, where further spread can occur.[39]
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.[40] 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,[41] orinstrumentation of the bladder orcolon.[36] Intermittent bacteremia is characterized by periodic seeding of the same bacteria into the bloodstream by an existing infection elsewhere in the body, such as anabscess,pneumonia, orbone infection, followed by clearing of that bacteria from the bloodstream. This cycle will often repeat until the existing infection is successfully treated.[36] Persistent bacteremia is characterized by the continuous presence of bacteria in the bloodstream.[36] It is usually the result of aninfected heart valve, acentral line-associated bloodstream infection (CLABSI), an infected blood clot (suppurative thrombophlebitis), or an infectedblood vessel graft.[36] Persistent bacteremia can also occur as part of the infection process oftyphoid fever,brucellosis, andbacterial meningitis. Left untreated, conditions causing persistent bacteremia can be potentially fatal.[17]
Bacteremia is clinically distinct fromsepsis, which is a condition where the blood stream infection is associated with aninflammatory response from the body, often causing abnormalities inbody temperature, heart rate, breathing rate, blood pressure, andwhite blood cell count.[42]
The presence of bacteria in the blood almost always requires treatment withantibiotics. This is because there are highmortality rates from progression tosepsis if antibiotics are delayed. This is especially the case if the sepsis gets worse, and even more if it becomes severe sepsis (where organ damage begins), septic shock (the organ damage continues, which lowers the blood pressure to the point where special drugs are needed to help keep it high enough), or multiple organ dysfunction syndrome (where organ damage can quickly become fatal, even with supportive devices).[27]
The treatment of bacteremia should begin withempiric antibiotic coverage. Any patient presenting with signs or symptoms of bacteremia or a positive blood culture should be started on intravenous antibiotics.[23] The choice of antibiotic is determined by the most likely source of infection and by the characteristic organisms that typically cause that infection. Other important considerations include the patient's history of antibiotic use, the severity of the presenting symptoms, and any allergies to antibiotics.[43] Empiric antibiotics should be narrowed, preferably to a single antibiotic, once the blood culture returns with a particular bacteria that has been isolated.[43]
TheInfectious Disease Society of America (IDSA) recommends treating uncomplicatedmethicillin resistant staph aureus (MRSA) bacteremia with a 14-day course of intravenous vancomycin.[44] Uncomplicated bacteremia is defined as having positive blood cultures for MRSA, but having no evidence of endocarditis, no implantedprostheses, negative blood cultures after 2–4 days of treatment, and signs of clinical improvement after 72 hrs.[44]
The antibiotic treatment of choice for streptococcal and enteroccal infections differs by species. However, it is important to look at the antibiotic resistance pattern for each species from the blood culture to better treat infections caused by resistant organisms.[13]
The treatment of gram negative bacteremia is also highly dependent on the causative organism. Empiric antibiotic therapy should be guided by the most likely source of infection and the patient's past exposure to healthcare facilities.[45] In particular, a recent history of exposure to a healthcare setting may necessitate the need for antibiotics withpseudomonas aeruginosa coverage or broader coverage for resistant organisms.[45] Extended generationcephalosporins such asceftriaxone orbeta lactam/beta lactamase inhibitor antibiotics such aspiperacillin-tazobactam are frequently used for the treatment of gram negative bacteremia.[45]
For healthcare-associated bacteremia due to intravenous catheters, the IDSA has published 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.[46] 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.[46]
{{cite book}}: CS1 maint: multiple names: authors list (link)