View source for Bloodstream infection

{{Short description|Bacterial or fungal infection of blood}}
{{for|the systemic immune response to bacterial infection in the blood|sepsis}}
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'''Bloodstream infections''' ('''BSIs''') are infections of [[blood]] caused by [[blood-borne pathogens]].<ref name="Viscoli">{{cite journal |last1=Viscoli |first1=C |title=Bloodstream Infections: The peak of the iceberg. |journal=Virulence |date=2 April 2016 |volume=7 |issue=3 |pages=248–51 |doi=10.1080/21505594.2016.1152440 |pmid=26890622|pmc=4871637 |doi-access=free }}</ref> The detection of [[microbe]]s in the blood (most commonly accomplished by [[blood culture]]s<ref>{{Cite web|url=https://www.uptodate.com/contents/blood-cultures-for-the-detection-of-bacteremia|title=Blood Cultures for the Detection of Bacteremia|last=Doern|first=Gary|date=September 13, 2016|website=uptodate.com|access-date=December 1, 2016}}</ref>) is always abnormal. A bloodstream infection is different from [[sepsis]], which is characterized by severe [[Inflammation|inflammatory]] or [[immune response]]s of the host organism to pathogens.<ref>{{Cite journal|last1=Fan|first1=Shu-Ling|last2=Miller|first2=Nancy S.|last3=Lee|first3=John|last4=Remick|first4=Daniel G.|date=2016-09-01|title=Diagnosing sepsis - The role of laboratory medicine|journal=Clinica Chimica Acta; International Journal of Clinical Chemistry|volume=460|pages=203–210|doi=10.1016/j.cca.2016.07.002|issn=1873-3492|pmc=4980259|pmid=27387712}}</ref>

Bacteria can enter the bloodstream as a severe complication of [[infection]]s (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]]).<ref>{{Cite journal|last1=Sligl|first1=Wendy|last2=Taylor|first2=Geoffrey|last3=Brindley|first3=Peter G.|date=2006-07-01|title=Five years of nosocomial Gram-negative bacteremia in a general intensive care unit: epidemiology, antimicrobial susceptibility patterns, and outcomes|journal=International Journal of Infectious Diseases |volume=10|issue=4|pages=320–325|doi=10.1016/j.ijid.2005.07.003|issn=1201-9712|pmid=16460982|doi-access=free}}</ref> Transient bacteremia can result after dental procedures or brushing of teeth.<ref name="Perez-Chaparro 300–303">{{Cite journal|last1=Perez-Chaparro|first1=P. J.|last2=Meuric|first2=V.|last3=De Mello|first3=G.|last4=Bonnaure-Mallet|first4=M.|date=2011-11-01|title=[Bacteremia of oral origin]|journal=Revue de Stomatologie et de Chirurgie Maxillo-Faciale|volume=112|issue=5|pages=300–303|doi=10.1016/j.stomax.2011.08.012|issn=1776-257X|pmid=21940028}}</ref>

Bacteremia can have several important health consequences. Immune responses to the bacteria can cause [[sepsis]] and [[septic shock]], which, particularly if severe sepsis and then septic shock occurs, have high [[mortality rate]]s, especially if not treated quickly (though, if treated early, currently mild sepsis can usually be dealt with successfully).<ref>{{Cite journal|last1=Singer|first1=Mervyn|last2=Deutschman|first2=Clifford S.|last3=Seymour|first3=Christopher Warren|last4=Shankar-Hari|first4=Manu|last5=Annane|first5=Djillali|last6=Bauer|first6=Michael|last7=Bellomo|first7=Rinaldo|last8=Bernard|first8=Gordon R.|last9=Chiche|first9=Jean-Daniel|date=2016-02-23|title=The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)|journal=JAMA|volume=315|issue=8|pages=801–810|doi=10.1001/jama.2016.0287|issn=1538-3598|pmc=4968574|pmid=26903338}}</ref> 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]].{{Citation needed|date=January 2021}} Treatment for bacteremia is with [[antibiotics]], and prevention with [[Antimicrobial prophylaxis|antibiotic prophylaxis]] can be given in high risk situations.<ref>{{Cite journal|last1=Yang|first1=Lu|last2=Tang|first2=Zhuang|last3=Gao|first3=Liang|last4=Li|first4=Tao|last5=Chen|first5=Yongji|last6=Liu|first6=Liangren|last7=Han|first7=Ping|last8=Li|first8=Xiang|last9=Dong|first9=Qiang|s2cid=6566177|date=2016-08-01|title=The augmented prophylactic antibiotic could be more efficacious in patients undergoing transrectal prostate biopsy: a systematic review and meta-analysis|journal=International Urology and Nephrology|volume=48|issue=8|pages=1197–1207|doi=10.1007/s11255-016-1299-7|issn=1573-2584|pmid=27160220}}</ref>

==Signs and symptoms==
Bacteremia is typically transient and is quickly removed from the blood by the [[immune system]].<ref name="Perez-Chaparro 300–303"/>

Bacteremia frequently evokes a response from the immune system called [[sepsis]], which consists of symptoms such as [[fever]], chills, and [[hypotension]].<ref name="Scott 1–9">{{Cite journal|last=Scott|first=Michael C.|date=2017-02-01|title=Defining and Diagnosing Sepsis|journal=Emergency Medicine Clinics of North America|volume=35|issue=1|pages=1–9|doi=10.1016/j.emc.2016.08.002|issn=1558-0539|pmid=27908326}}</ref> Severe immune responses to bacteremia may result in [[septic shock]] and ''[[multiple organ dysfunction syndrome]]'',<ref name="Scott 1–9"/> which are potentially fatal.

==Types==
Based on type of causative microbe, bloodstream infections are of many types:
{| {{table}}
! Type of blood-borne infection
! Causative microbe
! Description
! Examples
|-
| [[Bacteremia]]s
| [[Bacteria]]
| Bacteremia, in the strictest sense, refers to presence of [[wikt:viable#Noun|viable]] 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.<ref>{{Citation |last=Smith |first=David A. |title=Bacteremia |date=2023 |url=https://www.ncbi.nlm.nih.gov/books/NBK441979/ |work=StatPearls |access-date=2023-12-15 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=28723008 |last2=Nehring |first2=Sara M.}}</ref>
| {{blist|Meningitis, pneumonia, [[syphilis]], [[brucellosis]], [[endocarditis]]}}
|-
| [[Viremia]]s
| [[Virus]]es
| '''Viremia''' is a medical condition where [[virus]]es enter the [[blood]]stream and hence have access to the rest of the body. It is similar to ''[[bacteremia]]'', a condition where [[bacteria]] enter the bloodstream.<ref name="Sherris">{{cite book | veditors = Ryan KJ, Ray CG | title = Sherris Medical Microbiology | edition = 4th | publisher = McGraw Hill | year = 2004 | isbn = 978-0-8385-8529-0 | page = 881}}</ref> 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.
| {{blist|[[HIV-AIDS]], [[Ebola]], [[hepatitis B]], [[hepatitis C]]}}
|-
| [[Fungemia]]s
| [[Fungi]]
| '''Fungemia''' is the presence of [[fungus|fungi]] or [[yeast]]s in the [[blood]]. The most common type, also known as '''candidemia''', '''candedemia''', or '''systemic [[candidiasis]]''', is caused by ''[[Candida (fungus)|Candida]]'' species; candidemia is also among the most common bloodstream infections of any kind.<ref>{{Cite web|url=https://www.cdc.gov/fungal/diseases/candidiasis/invasive/statistics.html|title=Statistics|date=13 November 2019|website=Invasive Candidiasis|publisher=Centers for Disease Control and Prevention|location=United States|access-date=24 December 2019}}</ref> Infections by other fungi, including ''[[Saccharomyces]]'', ''[[Aspergillus]]'' (as in aspergillemia, also called invasive [[aspergillosiis]]) and ''[[Cryptococcus (fungus)|Cryptococcus]]'', are also called fungemia. It is most commonly seen in [[immunosuppressed]] or [[immunocompromised]] [[patient]]s with severe [[neutropenia]], [[cancer]] patients, or in patients with intravenous [[catheter]]s.
| [[Candidemia]], aspergillemia (invasive [[aspergillosis]])
|-
| [[Protozoemia]]<br />(blood-borne protozoal infections)
| [[Protozoa]]
| '''Protozoan infections''' are [[parasitic diseases]] caused by organisms formerly classified in the kingdom [[Protozoa]]. These organisms are now classified in the supergroups [[Excavata]], [[Amoebozoa]], [[Harosa]] (SAR supergroup), and [[Archaeplastida]]. They are usually contracted by either an insect vector or by contact with an infected substance or surface.<ref name="Prescott2020">{{Cite book|title=Prescott's Microbiology|last=Wiley, Sandman, Wood|first=K, J, D|publisher=McGraw-Hill Education|year=2020}}</ref>
| {{blist|[[Malaria]], [[giardia]], [[toxoplasmosis]], [[babesiosis]], [[trypanosomiasis]], [[leishmaniasis]]}}
|}

==Causes==
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 [[Health Care-Associated Infection|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).{{citation needed|date=August 2021}}

=== Gram positive bacteremia ===
[[Gram-positive bacteria|Gram positive bacteria]] are an increasingly important cause of bacteremia.<ref name="Cervera S26–30">{{Cite journal|last1=Cervera|first1=Carlos|last2=Almela|first2=Manel|last3=Martínez-Martínez|first3=José A.|last4=Moreno|first4=Asunción|last5=Miró|first5=José M.|date=2009-01-01|title=Risk factors and management of Gram-positive bacteraemia|journal=International Journal of Antimicrobial Agents|volume=34|issue=Suppl 4 |pages=S26–30|doi=10.1016/S0924-8579(09)70562-X|issn=1872-7913|pmid=19931813}}</ref> 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]].{{citation needed|date=August 2021}}

''[[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.<ref>{{Cite journal|last1=Biedenbach|first1=Douglas J.|last2=Moet|first2=Gary J.|last3=Jones|first3=Ronald N.|date=2004-09-01|title=Occurrence and antimicrobial resistance pattern comparisons among bloodstream infection isolates from the SENTRY Antimicrobial Surveillance Program (1997-2002)|journal=Diagnostic Microbiology and Infectious Disease|volume=50|issue=1|pages=59–69|doi=10.1016/j.diagmicrobio.2004.05.003|issn=0732-8893|pmid=15380279}}</ref> 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.<ref>{{Cite journal|last=Lowy|first=Franklin D.|date=1998-08-20|title=Staphylococcus aureus Infections|journal=New England Journal of Medicine|volume=339|issue=8|pages=520–532|doi=10.1056/NEJM199808203390806|issn=0028-4793|pmid=9709046}}</ref>

There are many different types of [[Streptococcus|streptococcal]] species that can cause bacteremia. [[Streptococcus pyogenes|''Group A streptococcus'']] (GAS) typically causes bacteremia from skin and soft tissue infections.<ref name="Current Medical Diagnosis">{{Cite book|title=Current Medical Diagnosis and Treatment 2017|last=Schwartz|first=Brian|publisher=McGraw Hill|year=2016|isbn=978-1-25-958511-1|location=New York|pages=Chapter 33}}</ref> [[Streptococcus agalactiae|''Group B streptococcus'']] is an important cause of bacteremia in [[Infant|neonates]], often immediately following birth.<ref name="Cohen-Poradosu">{{Cite book|title=Harrison's Principles of Internal Medicine 19th Edition|last=Cohen-Poradosu|first=Ronit|publisher=McGraw Hill|year=2015|isbn=978-0-07-180215-4|location=New York|pages=Chapter 201}}</ref> ''[[Viridans streptococci]]'' species are normal bacterial flora of the mouth. Viridans strep can cause temporary bacteremia after eating, toothbrushing, or flossing.<ref name="Cohen-Poradosu" /> More severe bacteremia can occur following dental procedures or in patients receiving chemotherapy.<ref name="Cohen-Poradosu" /> Finally, ''[[Streptococcus bovis]]'' is a common cause of bacteremia in patients with colon cancer.<ref>{{Cite book|title=Harrison's Principles of Internal Medicine 19th Edition|last=Mayer|first=Robert|publisher=McGraw Hill|year=2015|isbn=978-0-07-180215-4|location=New York|pages=Chapter 110}}</ref>

[[Enterococcus|''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 infection]]s and surgical wounds are all risk factors for developing bacteremia from enterococcal species.<ref>{{Cite book|title=Harrison's Principles of Internal Medicine 19th Edition|last=Arias|first=Cesar|publisher=McGraw Hill|year=2015|isbn=978-0-07-180215-4|location=New York|pages=Chapter 174}}</ref> [[Vancomycin-resistant Enterococcus|Resistant enterococcal]] species can cause bacteremia in patients who have had long hospital stays or frequent antibiotic use in the past (see [[antibiotic misuse]]).<ref>{{Cite book|title=Harrison's Manual of Medicine|last=Kasper|first=Dennis|publisher=McGraw Hill|year=2015|isbn=978-0-07-182852-9|location=New York|pages=Chapter 87}}</ref>

=== Gram negative bacteremia ===
[[Gram-negative bacteria|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.<ref>{{Cite journal|last1=Gaynes|first1=Robert|last2=Edwards|first2=Jonathan R.|last3=National Nosocomial Infections Surveillance System|date=2005-09-15|title=Overview of nosocomial infections caused by gram-negative bacilli|journal=Clinical Infectious Diseases|volume=41|issue=6|pages=848–854|doi=10.1086/432803|issn=1537-6591|pmid=16107985|doi-access=free}}</ref><ref>{{Cite journal|last1=Diekema|first1=D. J.|last2=Beekmann|first2=S. E.|last3=Chapin|first3=K. C.|last4=Morel|first4=K. A.|last5=Munson|first5=E.|last6=Doern|first6=G. V.|date=2003-08-01|title=Epidemiology and outcome of nosocomial and community-onset bloodstream infection|journal=Journal of Clinical Microbiology|volume=41|issue=8|pages=3655–3660|doi=10.1128/JCM.41.8.3655-3660.2003|issn=0095-1137|pmc=179863|pmid=12904371}}</ref> In general, gram negative bacteria enter the bloodstream from infections in the [[respiratory tract]], [[Genitourinary system|genitourinary tract]], gastrointestinal tract, or [[Biliary tract|hepatobiliary system]]. Gram-negative bacteremia occurs more frequently in elderly populations (65 years or older) and is associated with higher [[morbidity]] and mortality in this population.<ref name="Kevin High">{{Cite book|title=Geriatric Medicine and Gerontology 7th Edition|last=High|first=Kevin|publisher=McGraw Hill|year=2017|isbn=978-0-07-183345-5|location=New York|pages=Chapter 125}}</ref>[[Escherichia coli|''E.coli'']] is the most common cause of community-acquired bacteremia accounting for approximately 75% of cases.<ref>{{Cite journal|last1=Luzzaro|first1=F.|last2=Viganò|first2=E. F.|last3=Fossati|first3=D.|last4=Grossi|first4=A.|last5=Sala|first5=A.|last6=Sturla|first6=C.|last7=Saudelli|first7=M.|last8=Toniolo|first8=A.|last9=AMCLI Lombardia Hospital Infectious Study Group|s2cid=13043807|date=2002-12-01|title=Prevalence and drug susceptibility of pathogens causing bloodstream infections in northern Italy: a two-year study in 16 hospitals|journal=European Journal of Clinical Microbiology & Infectious Diseases|volume=21|issue=12|pages=849–855|doi=10.1007/s10096-002-0837-7|issn=0934-9723|pmid=12525919}}</ref> E.coli bacteremia is usually the result of a urinary tract infection. Other organisms that can cause community-acquired bacteremia include ''[[Pseudomonas aeruginosa]]'', ''[[Klebsiella pneumoniae]]'', and ''[[Proteus mirabilis]]''. ''[[Salmonella]]'' infection, despite mainly only resulting in gastroenteritis in the developed world, is a common cause of bacteremia in Africa.<ref>{{Cite journal|last1=Deen|first1=Jacqueline|last2=von Seidlein|first2=Lorenz|last3=Andersen|first3=Finn|last4=Elle|first4=Nelson|last5=White|first5=Nicholas J.|last6=Lubell|first6=Yoel|date=2012-06-01|title=Community-acquired bacterial bloodstream infections in developing countries in south and southeast Asia: a systematic review|journal=The Lancet. Infectious Diseases|volume=12|issue=6|pages=480–487|doi=10.1016/S1473-3099(12)70028-2|issn=1474-4457|pmid=22632186}}</ref> It principally affects children who lack antibodies to Salmonella and HIV+ patients of all ages.<ref>{{cite journal |last1=Kurtz |first1=Jonathan R |last2=Goggins |first2=J. Alan |last3=McLachlan |first3=James B. |date=October 2017 |title=Salmonella infection: Interplay between the bacteria and host immune system |journal=Immunology Letters |volume=190 |pages=42–50 |doi=10.1016/j.imlet.2017.07.006 |pmid=28720334 |pmc=5918639 }}</ref>

Among healthcare-associated cases of bacteremia, gram negative organisms are an important cause of bacteremia in the [[Intensive care unit|ICU]].<ref name="Peleg & Hooper">{{Cite journal|last1=Peleg|first1=Anton Y.|last2=Hooper|first2=David C.|date=2010-05-13|title=Hospital-Acquired Infections Due to Gram-Negative Bacteria|journal=The New England Journal of Medicine|volume=362|issue=19|pages=1804–1813|doi=10.1056/NEJMra0904124|issn=0028-4793|pmc=3107499|pmid=20463340}}</ref> Catheters in the veins, arteries, or urinary tract can all create a way for gram negative bacteria to enter the bloodstream.<ref name="Current Medical Diagnosis" /> Surgical procedures of the genitourinary tract, intestinal tract, or hepatobiliary tract can also lead to gram negative bacteremia.<ref name="Current Medical Diagnosis" /> ''Pseudomonas'' and [[Enterobacter|''Enterobacter'' species]] are the most important causes of gram negative bacteremia in the ICU.<ref name="Peleg & Hooper" />

=== Bacteremia risk factors ===
There are several risk factors that increase the likelihood of developing bacteremia from any type of bacteria.<ref name="Cervera S26–30"/><ref>{{Cite journal|last1=Graff|first1=Larissa R.|last2=Franklin|first2=Kristal K.|last3=Witt|first3=Lana|last4=Cohen|first4=Neal|last5=Jacobs|first5=Richard A.|last6=Tompkins|first6=Lucy|last7=Guglielmo|first7=B. Joseph|date=2002-02-15|title=Antimicrobial therapy of gram-negative bacteremia at two university-affiliated medical centers|journal=The American Journal of Medicine|volume=112|issue=3|pages=204–211|issn=0002-9343|pmid=11893347|doi=10.1016/s0002-9343(01)01092-0}}</ref> These include:
* [[HIV/AIDS|HIV infection]]
* [[Diabetes mellitus|Diabetes Mellitus]]
* Chronic [[hemodialysis]]
* Solid [[Organ transplantation|organ transplant]]
* [[Hematopoietic stem cell transplantation|Stem cell transplant]]
* Treatment with [[glucocorticoid]]s
* [[Liver failure]]
* [[Asplenia]]<ref>{{Cite journal|last=Brigden|first=M. L.|date=2001-02-01|title=Detection, education and management of the asplenic or hyposplenic patient|journal=American Family Physician|volume=63|issue=3|pages=499–506, 508|issn=0002-838X|pmid=11272299}}</ref>

==Mechanism==
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]]).<ref>{{Cite journal|last1=Agarwal|first1=Anil|last2=Aggarwal|first2=Aditya N.|s2cid=1561868|date=2016-08-01|title=Bone and Joint Infections in Children: Acute Hematogenous Osteomyelitis|journal=Indian Journal of Pediatrics|volume=83|issue=8|pages=817–824|doi=10.1007/s12098-015-1806-3|issn=0973-7693|pmid=26096866}}</ref>

Prosthetic cardiac implants (for example [[Artificial heart valve|artificial heart valves)]] are especially vulnerable to infection from bacteremia.<ref>{{Cite journal|last=Guay|first=David R.|date=2012-02-01|title=Antimicrobial prophylaxis in noncardiac prosthetic device recipients|journal=Hospital Practice|volume=40|issue=1|pages=44–74|doi=10.3810/hp.2012.02.947|issn=2154-8331|pmid=22406882|s2cid=10854052}}</ref> Prior to widespread use of vaccines, occult bacteremia was an important consideration in febrile children that appeared otherwise well.<ref>{{Cite web|url=https://www.uptodate.com/contents/fever-without-a-source-in-children-3-to-36-months-of-age|title=UpToDate|website=www.uptodate.com}}</ref>

==Diagnosis==
Bacteremia is most commonly diagnosed by [[blood culture]], in which a sample of blood drawn from the vein by needle puncture is allowed to [[Incubator (microbiology)|incubate]] with a [[microbiological medium|medium]] that promotes bacterial growth.<ref name="Coburn">{{Cite journal|last1=Coburn|first1=Bryan|last2=Morris|first2=Andrew M.|last3=Tomlinson|first3=George|last4=Detsky|first4=Allan S.|date=2012-08-01|title=Does This Adult Patient With Suspected Bacteremia Require Blood Cultures?|journal=JAMA|volume=308|issue=5|doi=10.1001/jama.2012.8262|pmid=22851117|issn=0098-7484|pages=502–11}}</ref> 
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|date=November 2021}}
Recent technical procedures enable the isolation of bacteria from whole blood within an hour without the need for blood culture, although these methods have been verified only for bacteria-spiked blood of healthy donors and not yet for septic patient samples.
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 }}</ref>

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.<ref name="Hall 788–802">{{Cite journal|last1=Hall|first1=Keri K.|last2=Lyman|first2=Jason A.|date=2016-12-16|title=Updated Review of Blood Culture Contamination|journal=Clinical Microbiology Reviews|volume=19|issue=4|pages=788–802|doi=10.1128/CMR.00062-05|issn=0893-8512|pmc=1592696|pmid=17041144}}</ref> 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|S''taphylococcus 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.{{citation needed|date=November 2021}}

Two blood cultures drawn from separate sites of the body are often sufficient to diagnose bacteremia.<ref name="Hall 788–802"/> 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.<ref name="Hall 788–802"/> 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.<ref name="Hall 788–802"/> The patient's skin is typically cleaned with an alcohol-based product prior to drawing blood to prevent contamination.<ref name="Hall 788–802"/> Blood cultures may be repeated at intervals to determine if persistent—rather than transient—bacteremia is present.<ref name="Hall 788–802"/>

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 as [[Skin and soft tissue infection|in the skin or soft tissue]], a state of immunosuppression, or any recent invasive procedures.<ref name="Coburn"/>

Ultrasound of the heart is recommended in all those with bacteremia due to ''[[Staphylococcus aureus]]'' to rule out [[infectious endocarditis]].<ref>{{cite journal|last1=Holland|first1=TL|last2=Arnold|first2=C|last3=Fowler VG|first3=Jr|title=Clinical management of Staphylococcus aureus bacteremia: a review.|journal=JAMA|date=1 October 2014|volume=312|issue=13|pages=1330–41|pmid=25268440|doi=10.1001/jama.2014.9743|pmc=4263314}}</ref>

===Definition===

Bacteremia is the presence of [[bacteria]] in the bloodstream that are alive and capable of reproducing. It is a type of bloodstream infection.<ref name="Seifert S238–S245">{{Cite journal|last=Seifert|first=Harald|date=2009-05-15|title=The Clinical Importance of Microbiological Findings in the Diagnosis and Management of Bloodstream Infections|journal=Clinical Infectious Diseases|language=en|volume=48|issue=Supplement 4|pages=S238–S245|doi=10.1086/598188|issn=1058-4838|pmid=19374579|doi-access=free}}</ref> Bacteremia is defined as either a primary or secondary process. In primary bacteremia, bacteria have been directly introduced into the bloodstream.<ref name="auto">{{Cite web|url=http://ocw.tufts.edu/Content/6/readings/207697|title=IDP200 Pathophysiology of Infectious Diseases, Fall 2004/2005 - Tufts OpenCourseWare|website=ocw.tufts.edu|access-date=2016-12-07}}</ref> [[Drug injection|Injection drug use]] may lead to primary bacteremia. In the hospital setting, use of blood vessel [[catheter]]s contaminated with bacteria may also lead to primary bacteremia.<ref name="auto"/> Secondary bacteremia occurs when bacteria have entered the body at another site, such as the cuts in the skin, or [[Mucous membrane|the mucous membranes]] of the lungs ([[Respiratory tract|respiratory]] tract), mouth or intestines ([[Gastrointestinal tract|gastrointestinal]] tract), [[Urinary system|bladder (urinary tract)]], or genitals.<ref>{{Cite book|title=Medical Microbiology, 27e|publisher=McGraw-Hill Education|year=2016|isbn=9780-0-71-82498-9|location=New York|pages=Chapter 9|via=accessmedicine.mhmedical.com/content.aspx?bookid=1551&Sectionid=94106209}}</ref> 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.<ref>{{Cite book|title=Sherris Medical Microbiology, 6e|publisher=McGraw-Hill|year=2014|isbn=9780-0-7-181821-6|location=New York|pages=Infectious Diseases: Syndromes and Etiologies|via=accessmedicine.mhmedical.com/content.aspx?bookid=1020&Sectionid=56968846}}</ref>

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.<ref>{{Cite book|title=Harrison's Principles of Internal Medicine, 19e|last=Cohen-Poradosu|first=Ronit|publisher=McGraw-Hill|year=2015|isbn=978-0-07-180215-4|location=New York|pages=Chapter 201|via=accessmedicine.mhmedical.com/content.aspx?bookid=1130&Sectionid=79736907}}</ref> 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,<ref>{{Cite journal|last1=Forner|first1=Lone|last2=Larsen|first2=Tove|last3=Kilian|first3=Mogens|last4=Holmstrup|first4=Palle|date=2006-06-01|title=Incidence of bacteremia after chewing, tooth brushing and scaling in individuals with periodontal inflammation|journal=Journal of Clinical Periodontology|language=en|volume=33|issue=6|pages=401–407|doi=10.1111/j.1600-051X.2006.00924.x|issn=1600-051X|pmid=16677328}}</ref> or [[Cystoscopy|instrumentation of the bladder]] or [[Colonoscopy|colon]].<ref name="Seifert S238–S245"/> Intermittent bacteremia is characterized by periodic seeding of the same bacteria into the bloodstream by an existing infection elsewhere in the body, such as an [[abscess]], [[pneumonia]], or [[Osteomyelitis|bone infection]], followed by clearing of that bacteria from the bloodstream. This cycle will often repeat until the existing infection is successfully treated.<ref name="Seifert S238–S245"/> Persistent bacteremia is characterized by the continuous presence of bacteria in the bloodstream.<ref name="Seifert S238–S245"/> It is usually the result of an [[Infective endocarditis|infected heart valve]], a [[Central venous catheter|central line-associated bloodstream infection (CLABSI)]], an infected blood clot (suppurative thrombophlebitis), or an infected [[Vascular bypass|blood vessel graft]].<ref name="Seifert S238–S245"/> Persistent bacteremia can also occur as part of the infection process of [[typhoid fever]], [[brucellosis]], and [[Meningitis|bacterial meningitis]]. Left untreated, conditions causing persistent bacteremia can be potentially fatal.<ref name="Cohen-Poradosu" />

Bacteremia is clinically distinct from [[sepsis]], which is a condition where the blood stream infection is associated with an [[inflammation|inflammatory]] response from the body, often causing abnormalities in [[Fever|body temperature]], heart rate, breathing rate, blood pressure, and [[Complete blood count|white blood cell count]].<ref>{{Cite journal|last=Kaplan, MD|first=Lewis|date=2016-08-16|title=Systemic Inflammatory Response Syndrome: Background, Pathophysiology, Etiology|url=http://emedicine.medscape.com/article/168943-overview?pa=gdxcETkDmptKtfQmQBhj5R9jmxYFH11JUVmLoUSKvyQIfoYQZtZjDwqZOIoSMcqXd/sGPYa+ToEoLjuhFnUEHw==#a3|journal=Medscape}}</ref>

== Treatment ==
The presence of bacteria in the blood almost always requires treatment with [[antibiotics]]. This is because there are high [[mortality rate]]s from progression to [[sepsis]] 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).<ref name="Peleg & Hooper" />

The treatment of bacteremia should begin with [[Empiric antibiotics|empiric antibiotic]] coverage. Any patient presenting with signs or symptoms of bacteremia or a positive blood culture should be started on intravenous antibiotics.<ref name="Kevin High" /> 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.<ref name="Hooper chapter 170">{{Cite book|title=Harrison's Principles of Internal Medicine 19th Edition|last=Hooper|first=David|publisher=McGraw Hill|year=2016|isbn=978-0-07-180215-4|location=New York|pages=Chapter 170}}</ref> Empiric antibiotics should be narrowed, preferably to a single antibiotic, once the blood culture returns with a particular bacteria that has been isolated.<ref name="Hooper chapter 170" />

===Gram positive bacteremia===
The [[Infectious Diseases Society of America|Infectious Disease Society of America]] (IDSA) recommends treating uncomplicated [[Methicillin-resistant Staphylococcus aureus|methicillin resistant staph aureus (MRSA)]] bacteremia with a 14-day course of intravenous vancomycin.<ref name="Liu e18–55">{{Cite journal|last1=Liu|first1=Catherine|last2=Bayer|first2=Arnold|last3=Cosgrove|first3=Sara E.|last4=Daum|first4=Robert S.|last5=Fridkin|first5=Scott K.|last6=Gorwitz|first6=Rachel J.|last7=Kaplan|first7=Sheldon L.|last8=Karchmer|first8=Adolf W.|last9=Levine|first9=Donald P.|date=2011-02-01|title=Clinical practice guidelines by the infectious diseases society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children|journal=Clinical Infectious Diseases|volume=52|issue=3|pages=e18–55|doi=10.1093/cid/ciq146|issn=1537-6591|pmid=21208910|doi-access=free}}</ref> Uncomplicated bacteremia is defined as having positive blood cultures for MRSA, but having no evidence of endocarditis, no implanted [[Prosthesis|prostheses]], negative blood cultures after 2–4 days of treatment, and signs of clinical improvement after 72 hrs.<ref name="Liu e18–55"/>

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.<ref name="Cervera S26–30" />

===Gram negative bacteremia===
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.<ref name="Russo chapter 186">{{Cite book|title=Harrison's Principles of Internal Medicine 19th Edition|last=Russo|first=Thomas|publisher=McGraw Hill|year=2016|isbn=978-0-07-180215-4|location=New York|pages=Chapter 186}}</ref> 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.<ref name="Russo chapter 186" /> Extended generation [[cephalosporin]]s such as [[ceftriaxone]] or [[Beta-lactam|beta lactam]]/[[Β-Lactamase inhibitor|beta lactamase inhibitor]] antibiotics such as [[Piperacillin/tazobactam|piperacillin-tazobactam]] are frequently used for the treatment of gram negative bacteremia.<ref name="Russo chapter 186" />

===Catheter-associated infections===
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.<ref name="Mermel et al.">{{Cite journal|last1=Mermel|first1=Leonard A.|last2=Allon|first2=Michael|last3=Bouza|first3=Emilio|last4=Craven|first4=Donald E.|last5=Flynn|first5=Patricia|last6=O'Grady|first6=Naomi P.|last7=Raad|first7=Issam I.|last8=Rijnders|first8=Bart J. A.|last9=Sherertz|first9=Robert J.|date=2009-07-01|title=Clinical practice guidelines for the diagnosis and management of intravascular catheter-related infection: 2009 Update by the Infectious Diseases Society of America|journal=Clinical Infectious Diseases|volume=49|issue=1|pages=1–45|doi=10.1086/599376|issn=1537-6591|pmc=4039170|pmid=19489710}}</ref> 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.<ref name="Mermel et al." />

==See also==
* [[Antibiotic prophylaxis]]
* [[Dental antibiotic prophylaxis]]
* [[Fungemia]]
* [[Viremia]]

==References==
{{Reflist}}

== External links ==
{{Medical resources
| DiseasesDB      =
| ICD10           = {{ICD10|A|49|9|a|30}} (NOS)
| ICD9            = {{ICD9|790.7}}
| ICDO            =
| OMIM            =
| MedlinePlus     =
| eMedicineSubj   =
| eMedicineTopic  =
| MeshID          = D016470
| ICD10CM         = {{ICD10CM|R78.81}}
}}
* [http://emedicine.medscape.com/article/961169-overview Bacteremia at Medscape eMedicine]

{{Infectious blood tests}}

[[Category:Bacterial diseases]]
[[Category:Abnormal clinical and laboratory findings for blood]]
[[Category:Sepsis]]