Bacteremia
| Bacteremia | |
| ICD-10 | A49.9 (NOS) |
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| ICD-9 | 790.7 |
| MeSH | D016470 |
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Overview
Bacteremia is the presence of viable bacteria in the bloodstream. It may be transient or persistent and may occur with or without clinical manifestations. Bacteremia is distinct from bloodstream infection (BSI), a broader clinical concept encompassing clinically significant infection associated with microorganisms recovered from blood, and from sepsis, which is defined by life-threatening organ dysfunction caused by a dysregulated host response to infection.[1][2]
Bacteremia may result from an intravascular catheter, another localized infection, or a procedure and can permit hematogenous dissemination to distant sites. Clinical significance depends on the organism, source, persistence of bacteremia, host factors, and evidence of metastatic or endovascular infection.[1]
Clinical significance
Bacteremia should prompt evaluation for the source of infection, clinical severity, and whether infection has disseminated or involves an endovascular focus. Bacteremia may accompany sepsis or septic shock, but bacteremia alone does not establish either diagnosis.[2]
Potential complications include hematogenous seeding of distant organs and endovascular infection, including endocarditis. The probability of complications varies substantially by organism and clinical context; detailed organism-specific evaluation is addressed in dedicated microchapters.
Diagnosis
Blood cultures
Blood culture is the principal diagnostic test for bacteremia. Blood culture collection should use meticulous aseptic technique because contamination can produce false-positive results and lead to unnecessary treatment and additional testing.[3]
When bacteremia is suspected, blood cultures should be obtained before antimicrobial therapy when this can be accomplished without clinically important delay; in sepsis, collection should not delay antimicrobials by more than about 45 minutes. For adults, 20–30 mL of blood per culture set distributed across aerobic and anaerobic bottles, and generally two (sometimes 3–4) sets per septic episode, are recommended, with blood volume being the single most important determinant of yield.[3][4] Whether to collect from multiple sites, the traditional approach that aids contaminant discrimination, or a single site, favored by 2025 German national guidance to optimize fill volume and reduce contamination, remains an area of current guideline disagreement.[5]
Interpreting positive blood cultures
A positive blood culture should be interpreted in clinical context. Organism identity, number of positive bottles or sets, clinical syndrome, presence of intravascular devices, and time course help distinguish true bacteremia from contamination.
A positive result is more likely to reflect contamination when a single set grows a common skin commensal, such as coagulase-negative staphylococci. Discordant growth in only one of two bottles has a negative predictive value of approximately 98% for true coagulase-negative staphylococcal bacteremia, and a longer time-to-positivity, beyond approximately 20 hours, also favors contamination.[6]
Follow-up blood cultures
Follow-up blood cultures are not routinely required for every episode of bacteremia. They should be obtained selectively when persistence would alter management or when the organism or clinical syndrome has a substantial association with persistent bloodstream infection.[5]
Follow-up cultures to document clearance are recommended for Staphylococcus aureus, Staphylococcus lugdunensis, and Candida species, and should guide evaluation for persistent or complicated infection.[5]
Additional indications for repeat cultures may include suspected endovascular infection, an intravascular catheter or other endovascular source, persistent clinical findings suggesting ongoing infection, or other circumstances in which persistent bacteremia would change management.[5]
The value of follow-up cultures in gram-negative bacteremia is debated. Some cohort data suggest routine repeat cultures add little in uncomplicated, appropriately treated gram-negative BSI and increase unnecessary testing.[7] In contrast, two meta-analyses found that obtaining follow-up cultures in gram-negative BSI was independently associated with lower mortality (pooled OR 0.58, 95% CI 0.49–0.70), likely by identifying persistent bacteremia that warrants source-control or regimen changes.[8][9] Independent risk factors for persistent gram-negative bacteremia include end-stage renal disease, central venous catheter, extended-spectrum β-lactamase-producing organisms, resistance to empiric therapy, and unfavorable response at 48 hours.[8]
Management principles
Management requires both effective antimicrobial therapy and source evaluation and control. Antimicrobial selection should be guided by the suspected source, severity of illness, likely pathogens, local resistance patterns, subsequent susceptibility results, and patient-specific factors. Detailed empiric and organism-specific regimens belong in the Medical Therapy and organism-specific microchapters.
In patients with sepsis or septic shock, antimicrobial treatment and source-control decisions should follow current sepsis guidance and should not be delayed by unnecessary diagnostic procedures.[5]
Duration of antimicrobial therapy
Treatment duration should be individualized according to the organism, source, adequacy of source control, clinical response, presence of metastatic or endovascular infection, prosthetic material, and host factors.
For the population eligible for the BALANCE trial, 7 days of antibiotic therapy was noninferior to 14 days for mortality in adults with bloodstream infection.[10]
The 2026 post-hoc BALANCE analysis supports 7 days as the standard of care for uncomplicated non-Staphylococcus aureus bloodstream infection in the eligible population, while excluding important groups such as severe immunocompromise, prosthetic valves or endovascular grafts, and Staphylococcus aureus bacteremia.[11] Detailed duration selection and exceptions belong in the Medical Therapy microchapter.
Complications and source control
Bacteremia can result in hematogenous dissemination and secondary infection of distant sites. Persistent bacteremia should increase concern for an uncontrolled source, endovascular infection, or metastatic infection.[1]
In Staphylococcus aureus bacteremia, validated risk tools such as VIRSTA can help identify patients at low risk for infective endocarditis; a low-risk VIRSTA classification has reported a negative predictive value of approximately 99.3–99.5%.[12] Detailed endocarditis risk assessment and echocardiographic evaluation are addressed in the dedicated microchapter.
Source-control assessment should include consideration of infected intravascular catheters and other potentially removable or drainable foci when clinically appropriate. Detailed catheter-related bloodstream infection prevention, diagnosis, and management are addressed in dedicated microchapters.
See also
References
- ↑ 1.0 1.1 1.2 Holmes CL, Albin OR, Mobley HLT, Bachman MA (2025). "Bloodstream infections: mechanisms of pathogenesis and opportunities for intervention". Nature Reviews Microbiology. 23 (4): 210–224. doi:10.1038/s41579-024-01105-2. PMC PMC12519459 Check
|pmc=value (help). - ↑ 2.0 2.1 Singer M, Deutschman CS, Seymour CW; et al. (2016). "The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)". JAMA. 315 (8): 801–810. doi:10.1001/jama.2016.0287.
- ↑ 3.0 3.1 Miller JM, Binnicker MJ, Campbell S; et al. (2024). "Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM)". Clinical Infectious Diseases. doi:10.1093/cid/ciae104.
- ↑ O'Grady NP, Alexander E, Alhazzani W; et al. (2023). "Society of Critical Care Medicine and the Infectious Diseases Society of America Guidelines for Evaluating New Fever in Adult Patients in the ICU". Critical Care Medicine. 51 (11): 1570–1586. doi:10.1097/CCM.0000000000006022.
- ↑ 5.0 5.1 5.2 5.3 5.4 Prescott HC, Antonelli M, Alhazzani W; et al. (2026). "Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2026". Critical Care Medicine. 54 (4): 725–812. doi:10.1097/CCM.0000000000007075.
- ↑ Ben-Chetrit E, Helvitz Y, Levin PD (2026). "Diagnostic Value of Blood Culture Growth Patterns in Distinguishing Contaminants From Pathogens". Journal of Clinical Microbiology. PMID 41568951 Check
|pmid=value (help). - ↑ Wiggers JB, Xiong W, Daneman N (2016). "Sending repeat cultures: is there a role in the management of bacteremic episodes? (SCRIBE study)". BMC Infectious Diseases. 16: 286. doi:10.1186/s12879-016-1622-z. PMC 4906775.
- ↑ 8.0 8.1 Gatti M, Bonazzetti C, Tazza B; et al. (2023). "Impact on Clinical Outcome of Follow-Up Blood Cultures and Risk Factors for Persistent Bacteraemia in Patients With Gram-Negative Bloodstream Infections: A Systematic Review With Meta-Analysis". Clinical Microbiology and Infection. 29 (9): 1150–1158. doi:10.1016/j.cmi.2023.02.024.
- ↑ Thaden JT, Cantrell S, Dagher M; et al. (2022). "Association of Follow-up Blood Cultures With Mortality in Patients With Gram-Negative Bloodstream Infections: A Systematic Review and Meta-analysis". JAMA Network Open. 5 (9): e2232576. doi:10.1001/jamanetworkopen.2022.32576.
- ↑ BALANCE Investigators, for the Canadian Critical Care Trials Group, the Association of Medical Microbiology and Infectious Disease Canada Clinical Research Network, the Australian and New Zealand Intensive Care Society Clinical Trials Group, the Australasian Society for Infectious Diseases Clinical Research Network; et al. (2025). "Antibiotic Treatment for 7 versus 14 Days in Patients with Bloodstream Infections". The New England Journal of Medicine. 392 (11): 1065–1078. doi:10.1056/NEJMoa2404991.
- ↑ Ong SWX, Pinto R, Mahar RK; et al. (2026). "Accounting for Non-Adherence to Assigned Antibiotic Treatment Duration for Bloodstream Infection (BALANCE): A Post-Hoc Analysis of a Randomised Clinical Trial". The Lancet Infectious Diseases. 26 (3): 250–259. doi:10.1016/S1473-3099(25)00592-4. PMID 41237792 Check
|pmid=value (help). - ↑ Peinado-Acevedo JS, Hurtado-Guerra JJ, Hincapié C; et al. (2021). "Validation of VIRSTA and Predicting Risk of Endocarditis Using a Clinical Tool (PREDICT) Scores to Determine the Priority of Echocardiography in Patients With Staphylococcus Aureus Bacteremia". Clinical Infectious Diseases. 73 (5): e1151–e1157. doi:10.1093/cid/ciaa1844.