Detailed Analysis of the Characteristics of Sample Volume in Blood Culture Bottles

Estimating bacterial load in S. aureus and E. coli bacteremia using bacterial growth graph from the continuous monitoring blood culture system

BACKGROUND

We examined whether the time to positivity (TTP) and growth and detection plot graph (GDPG) created by the automated blood culture system can be used to determine the bacterial load in bacteremic patients and its potential association correlation with disease severity.

METHODS

Known bacterial inocula were injected into the blood culture bottles. The GDPGs for the specific inocula were downloaded and plotted. A cohort of 30 consecutive clinical cultures positive for S. aureus and E. coli was identified. Bacterial load was determined by comparing the GDPG with the "standard" curves. Variables associated with disease severity were compared across 3 bacterial load categories (< 100, 100-1000, > 1000 CFU/mL).

RESULTS

S. aureus growth was sensitive to the blood volume obtained whereas E. coli growth was less so. A 12-hour delay in sample transfer to the microbiology laboratory resulted in a decrease in TTP by 2-3 h. Mean TTP was 15 and 10 h for S. aureus and E. coli, respectively, which correlates with > 1000 CFU/mL and 500-1000 CFU/ml. For S. aureus, patients with a bacterial load > 100 CFU/mL had a higher mortality rate, (OR for death = 9.7, 95% CI 1.6-59, p = 0.01). Bacterial load > 1000 CFU/mL had an odds ratio of 6.4 (95% CI1.2-35, p = 0.03) to predict an endovascular source. For E. coli bacteremia, we did not find any correlations with disease severity.

CONCLUSION

GDPG retrieved from the automated blood culture system can be used to estimate bacterial load. S.aureus bacterial load, but not E.coli, was associated with clinical outcome.

Microbiological performance and adherence in blood culture protocols: The role of a second anaerobic bottle

Background

Bacteremia represents high rates of morbidity and mortality, especially in developing countries, highlighting the need for a diagnostic method that allows prompt and appropriate patient treatment. This study compared microbiological performance and adherence of two blood culture protocols for the diagnosis of bacteremia.

Methods

Quasi-experimental study conducted between June 2022 and February 2023. Two blood culture protocols were evaluated. Protocol 1 included two aerobic bottles and one anaerobic bottle. Protocol 2 included two aerobic and two anaerobic bottles. Protocols were analyzed in three phases: evaluation of protocol 1 (Phase 1); evaluation of protocol 1 plus educational activities for healthcare staff (Phase 2) and evaluation of protocol 2 (Phase 3).

Results

342 patients and 1155 blood culture bottles (732 aerobic and 423 anaerobic) were included. Positivity was 17.6 %, 22.8 % and 19.4 % in phases 1, 2 and 3, respectively. Among patients with bacteremia, 84.5 % had positive anaerobic bottles, with 9.9 % showing growth only in this bottle. The contamination rates were 1.9 %, 0.3 %, and 0.8 % for each phase, mainly in aerobic bottles. Median positivity time was 11 h for both bottes aerobic and anaerobic. Overall nursing adherence increased from 13.1 % in Phase 1, 25.9 % in Phase 2, and 28.1 % in Phase 3 (p = 0.009).

Conclusions

The findings indicate that adding a second anaerobic bottle does not enhance blood culture positivity. Rather than increasing bottle quantity, staff training might be a more effective approach to optimize results.

Deficits in blood culture collection in the emergency department if sepsis is suspected: results of a retrospective cohort study

PURPOSE

Blood cultures (BCs) are key for pathogen detection in septic patients. We investigated the extent to which sampling was performed and what factors were associated with the absence of general or inadequate BC sampling.

METHODS

We conducted a retrospective cohort study of hospitalized patients with sepsis admitted to one of three EDs in 2018. Primary outcome was the extent of general BC collection of at least 1 set. Secondary outcome was the extent of adequate BC sampling, defined as ≥ 2 sets before antibiotic therapy (AT). Multivariable logistic regression analysis was performed to identify factors associated with deficits in both outcomes.

RESULTS

1143 patients were analyzed. BCs were collected from 946 patients. Single BCs were taken from 520 patients, ≥ 2 sets from 426 patients. Overall, ≥ 2 BCs were taken from 349 patients before AT. BC sampling before AT occurred significantly more frequently when ≥ 2 BC sets were taken rather than a single one (81.9%, versus 68.4%, p < 0.001) and this also led to the highest pathogen detection rate in our cohort (65.6%). A body temperature of ≥ 38 °C was the a supporting factor for general and adequate BC collection in all three EDs. Retrospective analysis of 533 patients showed that the qSOFA score had no influence on general or adequate BC collection.

CONCLUSION

Data on everyday clinical practice in the pre-analytical phase of microbiological diagnostics shows considerable deficits and indicates the need for more implementation of best practice. The variations identified in BC sampling between EDs should be further investigated.

An emergency department intervention to improve earlier detection of community-onset bloodstream infection among hospitalized patients

BACKGROUND

Blood cultures (BCs) are essential microbiologic tests, but blood culturing diagnostic stewardship is frequently poor. We aimed to study the process-related failures and to evaluate the effect of an emergency department (ED) intervention on BCs collection practices and yield.

METHODS

We implemented an ED-quality improvement intervention including educational sessions, phlebotomists addition, promoting single-site strategy for BC-collection and preanalytical data feedback. BC-bottles collected, positive BCs, blood volumes and documentation of collection times were measured, before (December 2021-August 2022) and after (September 2022-July 2023) intervention. Results were corrected to hospitalizations admissions or days. We used interrupted-time series analyses for comparisons.

RESULTS

A total of 64,295 BC bottles were evaluated, 26,261 before and 38,034 postintervention. The median ED-BCs collected per week increased from 88 to 105 BCs (P < .0001), resulting from increased early sampling (P = .0001). Solitary BCs decreased (95%-28%), documented times increased (2.8%-25%), and average blood volume increased (3 mL to 4.5 mL) postintervention. Community-onset Bloodstream infections (BSIs) increased (39.6-52 bottles/1,000 admissions, P = .0001), while Health care-associated BSIs decreased (39-27 bottles/10,000 days, P = .0042). Contamination rates did not change.

CONCLUSIONS

An ED-focused intervention based on the education sessions and single-site strategy improved culturing stewardship and facilitated the early identification of BSI without an increase in contamination.

ddPCR enables rapid detection of bloodstream infections in patients on home parenteral nutrition: A prospective cohort study

INTRODUCTION

Chronic intestinal failure patients (CIF) require a central venous access device (CVAD) to administer parenteral nutrition. Most serious complication related to a CVAD is a central line-associated bloodstream infection (CLABSI). The golden standard to diagnose a CLABSI are blood cultures, however, they may require 1-5 days before getting a result. Droplet digital polymerase chain reaction (ddPCR) for the detection of pathogen 16S/28S rRNA is a novel culture-independent molecular technique that has been developed to enhance and expedite infection diagnostics within two and a half hours. In this study, we prospectively compared ddPCR with blood cultures to detect pathogens in whole blood.

METHODS

We included adult CIF patients with a clinical suspicion of CLABSI in this prospective single-blinded clinical study. Blood cultures were routinely collected and subsequently two central samples from the CVAD and two peripheral samples from a peripheral venous access point. Primary outcome was the sensitivity and specificity of ddPCR.

RESULTS

In total, 75 patients with 126 suspected CLABSI episodes were included, with 80 blood samples from the CVAD and 114 from peripheral veins. The central ddPCR samples showed a sensitivity of 91% (95%CI 77-98), and specificity of 96% (95%CI 85-99). Peripheral ddPCR samples had a sensitivity of 63% (95%CI 46-77) and specificity of 99% (95%CI 93-100).

CONCLUSION

ddPCR showed a high sensitivity and specificity relative to blood cultures and enables rapid pathogen detection and characterization. Clinical studies should explore if integrated ddPCR and blood culture outcomes enables a more rapid pathogen guided CLABSI treatment and enhancing patient outcomes.

Relationship between blood culture time to positivity, mortality rate, and severity of bacteremia

OBJECTIVES

We investigated the association between patient severity or mortality and time to positivity in bacteremia caused by various pathogens.

PATIENTS AND METHODS

This single-center retrospective study included patients with positive blood culture results.

RESULTS

Longer time to positivity was associated with 30-day mortality for Staphylococcus aureus (221 cases, time to positivity: 17.4 h in the 30-day mortality group vs. 14.1 h in the survival group). Age, chronic kidney disease, cerebrovascular disease, hypertensive drug use, consciousness disorder, and minimal systolic blood pressure were significant predictors of 30-day mortality. For S. aureus, mortality within 30 days was significantly higher when time to positivity was > 24 h (p = 0.04). The time to positivity of Streptococcus pneumoniae, α, β-hemolytic Streptococcus, Enterococcus sp., Enterobacteriaceae, glucose-nonfermenting Gram-negative rods, Candida sp., and anaerobe was not significantly associated with 30-day mortality.

CONCLUSIONS

Among various pathogens, time to positivity > 24 h was associated with 30-day mortality for S. aureus.

Intermittent hemodialysis: a review of the top antimicrobial stewardship practices to be employed

The vulnerability of patients on hemodialysis (HD) to infections is evident by their increased susceptibility to infections in general and to resistant organisms in particular. Unnecessary, inappropriate, or suboptimal antimicrobial prescribing is common in dialysis units. This underscores the need for dedicated antimicrobial stewardship (AMS) interventions that can be implemented both in the inpatient and outpatient settings. In this review, we provide a comprehensive approach for clinicians with the most updated coordinated AMS principles in HD setting in six areas: prevention, diagnosis, treatment, education and empowerment, monitoring, and research.

Optimizing Blood Culture Collection Volumes

ABSTRACT

Infection in an immunocompromised person can be a life-threatening emergency. Collection of blood culture specimens is an important method for detecting organisms when infection is suspected. One aspect of proper blood culture collection is obtaining an accurate blood volume in the sample in accordance with the blood culture bottle manufacturer's recommendation. Underfilling the culture bottle can lead to false-negative results, while overfilling it can lead to false-positive results. At our institution, the Department of Laboratory Medicine (DLM) routinely monitors blood culture bottle volumes and notifies the nursing department of underfill/overfill events, which the department then reviews. Over several years, the DLM and the nursing department noted an increase in these events. A clinical nurse specialist and three staff nurses in the oncology/critical care services area partnered with the DLM to determine why. Upon investigation, two key issues-imprecise weighing of bottles and staff misunderstanding of the proper blood culture collection technique-were discovered. In response, the nursing standard of practice and guidance on the DLM webpage were updated and nursing education was performed. As a result, underfill/overfill events decreased by 71% in a little over a year.

Subculturing and Gram staining of blood cultures flagged negative by the BACTEC™ FX system: Optimizing the workflow for detection of Cryptococcus neoformans in clinical specimens

Objective

To investigate whether an incubation time of 5 days (Aerobic/F, Anaerobic/F) and 14 days (Myco/F) blood culture bottles is sufficient to prevent false-negative results.

Methods

We evaluated 1,244 blood bottles (344 patients) defined as negative by the BACTEC™ FX system. We also reviewed published cases and our own cases of bloodstream infection caused by Cryptococcus neoformans and simulated different scenarios, including different inoculation concentrations, bottle types, and clinical isolates.

Results

Two bottles (0.16%) were found to contain C. neoformans when subcultured and Gram stained. A 5-day protocol with Aerobic/F bottles was insufficient for the growth of C. neoformans in some cases, and C. neoformans grew better in Myco/F bottles than in Aerobic/F bottles.

Conclusion

Subculturing and Gram staining after a 5-day protocol were important for the detection of C. neoformans, and Myco/F bottles should be collected for the blood culture of C. neoformans.

Factors impacting the pre-analytical quality of blood cultures-Analysis at a tertiary medical center

BACKGROUND

Blood cultures (BC) are critical for the diagnosis of bloodstream infections, pathogen identification, and resistance testing. Guidelines recommend a blood volume of 8-10 mL per bottle as lower volumes result in decreased sensitivity. We aimed to evaluate factors for non-adherence to recommended volumes and assess the effects on diagnostic performance.

METHODS

From February to April 2020, we measured collected blood volumes by weighing all BC containers from inpatient samples at the University Hospital Basel. Information on BC volumes was merged with clinical and microbiological data, as well as nursing staff schedules. We analyzed factors associated with (i) BC sampling volume, (ii) reaching recommended volumes (≥8 mL), (iii) BC positivity, and (iv) time to positivity using linear and generalized linear mixed effect models.

RESULTS

We evaluated a total of 4'118 BC bottles collected from 686 patients. A total of 1'495 (36.3%) of all bottles contained the recommended filling volume of ≥8 mL. Using a central venous and arterial catheter for drawing blood resulted in an increase of filling volume by 0.26 mL (95% CI 0.10, 0.41) and 0.50 mL (95% CI 0.31, 0.69) compared to peripheral venipuncture, respectively. Each additional nursing staff working at the time of blood drawing was associated with 6% higher odds of achieving the recommended filling volume. We found no significant correlation between the filling volume and the positivity rate.

CONCLUSION

Our results indicate critical pre-analytical quality markers linked to BC collection procedures to reach recommended collection volumes. No significant impact on the positivity rate was found.

Using a 29-mRNA Host Response Classifier To Detect Bacterial Coinfections and Predict Outcomes in COVID-19 Patients Presenting to the Emergency Department

Clinicians in the emergency department (ED) face challenges in concurrently assessing patients with suspected COVID-19 infection, detecting bacterial coinfection, and determining illness severity since current practices require separate workflows. Here, we explore the accuracy of the IMX-BVN-3/IMX-SEV-3 29 mRNA host response classifiers in simultaneously detecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and bacterial coinfections and predicting clinical severity of COVID-19. A total of 161 patients with PCR-confirmed COVID-19 (52.2% female; median age, 50.0 years; 51% hospitalized; 5.6% deaths) were enrolled at the Stanford Hospital ED. RNA was extracted (2.5 mL whole blood in PAXgene blood RNA), and 29 host mRNAs in response to the infection were quantified using Nanostring nCounter. The IMX-BVN-3 classifier identified SARS-CoV-2 infection in 151 patients with a sensitivity of 93.8%. Six of 10 patients undetected by the classifier had positive COVID tests more than 9 days prior to enrollment, and the remaining patients oscillated between positive and negative results in subsequent tests. The classifier also predicted that 6 (3.7%) patients had a bacterial coinfection. Clinical adjudication confirmed that 5/6 (83.3%) of the patients had bacterial infections, i.e., Clostridioides difficile colitis (n = 1), urinary tract infection (n = 1), and clinically diagnosed bacterial infections (n = 3), for a specificity of 99.4%. Two of 101 (2.8%) patients in the IMX-SEV-3 "Low" severity classification and 7/60 (11.7%) in the "Moderate" severity classification died within 30 days of enrollment. IMX-BVN-3/IMX-SEV-3 classifiers accurately identified patients with COVID-19 and bacterial coinfections and predicted patients' risk of death. A point-of-care version of these classifiers, under development, could improve ED patient management, including more accurate treatment decisions and optimized resource utilization. IMPORTANCE We assay the utility of the single-test IMX-BVN-3/IMX-SEV-3 classifiers that require just 2.5 mL of patient blood in concurrently detecting viral and bacterial infections as well as predicting the severity and 30-day outcome from the infection. A point-of-care device, in development, will circumvent the need for blood culturing and drastically reduce the time needed to detect an infection. This will negate the need for empirical use of broad-spectrum antibiotics and allow for antibiotic use stewardship. Additionally, accurate classification of the severity of infection and the prediction of 30-day severe outcomes will allow for appropriate allocation of hospital resources.

The diagnostic value of next-generation sequencing technology in sepsis

Objective

This study aims to assess the clinical utility of next-generation sequencing (NGS) in sepsis diagnosis.

Methods

A prospective study was conducted on patients with a high suspicion of sepsis by unknown pathogens from January 2017 to December 2021. Blood samples were taken from patients to perform NGS, blood culture (BC), leucocyte (WBC), procalcitonin (PCT), creatinine (CREA), Albumin (ALB) and C-reactive protein (CRP) tests.

Results

The feedback time for BC was 3~5 days for bacteria and 5~7 days for fungi, while the turnover time for NGS was only 24 h. The clinical diagnosis was considered the “gold standard”. 83 patients passed our inclusion criteria and were separated into two groups by clinical diagnosis. 62 met the clinical diagnosis criteria for sepsis and 21 were non-sepsis. The data from the two groups were retrospectively compared and analyzed. Of 62 sepsis in 83 patients, 8(9.64%) were diagnosed by both BC and NGS, 51 (61.45%) by NGS only, 1(1.20%) by BC and 2 (2.41%) by conventional testing only; PCT, CREA, CRP levels and the detection rate of NGS and BC were higher in the sepsis group than in the non-sepsis group, while ALB levels were lower (p&lt;0.05). The logistic regression results in our study revealed that NGS and ALB were independent prediction factors for sepsis (p&lt;0.05), the area under the receiver operating characteristic curve (AUC), sensitivity and specificity of NGS for diagnosing sepsis was 0.857, 95.16% and 76.19%, while ALB was 0.728, 58.06%, 80.95%, respectively. The combination’s sensitivity, specificity and AUC of NGS and ALB were 93.55%, 85.71% and 0.935, greater than that of Albumin or NGS only (both p&lt;0.05).

Conclusion

NGS can effectively and quickly identify pathogens, thereby emerges as a promising technology for sepsis diagnosis. Combination of NGS and ALB can be used for early screening and is more powerful than NGS or ALB only.

Revisiting factors associated with blood culture positivity: Critical factors after the introduction of automated continuous monitoring blood culture systems

Blood culture is the main tool used to identify causative pathogens. Adequate volume and number of culture sets are considered key to blood culture positivity rate. It is not known whether these factors remain critical to the positivity rate after the introduction of automated continuous blood culture system monitoring. We measured blood volume per bottle and described the distribution of blood volume and number of culture sets. Multivariate logistic regression was performed to determine the independent association of blood volume, number of culture sets, diagnosis of sepsis in a patient, and other covariates with blood culture results. Only 6.9% of the blood culture bottle volumes complied with the guidance (8-10 mL), with the highest culture positivity rate (18%). Of the culture events, only one set of blood was cultured in 60.9% of events. In the multivariate analysis, blood culture volume per event (odds ratio [OR], 1.09 [95% confidence interval [CI], 1.06-1.11]), patients with a diagnosis of sepsis (OR, 2.86 [95% CI, 2.06-3.98]), and samples from the emergency department (OR, 2.29 [95% CI, 1.72-3.04]), but not the number of culture sets (OR, 0.74 [95% CI, 0.50-1.12]), were observed to be statistically significant with respect to blood culture positivity rate. Our results revealed that the total blood culture volume and the diagnosis of sepsis were critical factors affecting blood culture positivity rate. However, the proportion of blood culture bottles with the optimal blood volume was very low, and optimizing blood volume would be key to increasing blood culture positivity rate.

Effects of Blood Culture Aerobic/Anaerobic Bottle Collection Patterns from Both Sides of the Body on Positive Blood Culture Rate and Time-to-Positivity

Background

Although the principles for blood cultures (BCs) guidelines provide a recommendation for collection patterns, the complexity of clinical practice occasionally prompts clinicians to adopt non-standard collection patterns. Here, we investigate the influences of different BC collection patterns on detection of pathogens.

Methods

The BC collection patterns of 96 hospitals were surveyed online. And a retrospective study of BC data from a tertiary hospital was conducted.

Results

The results showed that 53.1% of hospitals adopted the recommended patterns. Among the 1439 episodes of true-positive BCs, 67.4% were found in both the left- and right-sided bottles; 58.2% were found in both aerobic and anaerobic bottles.

Conclusion

The present study suggested that the rate of standard collection patterns of blood culture was low and the non-standard collection patterns were associated with decreased detection of pathogens. Simultaneous collection of blood on the left and right sides was recommended as an effective pattern of BC collection.

Diagnosis of Bloodstream Infections: An Evolution of Technologies towards Accurate and Rapid Identification and Antibiotic Susceptibility Testing

Bloodstream infections (BSI) are a leading cause of death worldwide. The lack of timely and reliable diagnostic practices is an ongoing issue for managing BSI. The current gold standard blood culture practice for pathogen identification and antibiotic susceptibility testing is time-consuming. Delayed diagnosis warrants the use of empirical antibiotics, which could lead to poor patient outcomes, and risks the development of antibiotic resistance. Hence, novel techniques that could offer accurate and timely diagnosis and susceptibility testing are urgently needed. This review focuses on BSI and highlights both the progress and shortcomings of its current diagnosis. We surveyed clinical workflows that employ recently approved technologies and showed that, while offering improved sensitivity and selectivity, these techniques are still unable to deliver a timely result. We then discuss a number of emerging technologies that have the potential to shorten the overall turnaround time of BSI diagnosis through direct testing from whole blood-while maintaining, if not improving-the current assay's sensitivity and pathogen coverage. We concluded by providing our assessment of potential future directions for accelerating BSI pathogen identification and the antibiotic susceptibility test. While engineering solutions have enabled faster assay turnaround, further progress is still needed to supplant blood culture practice and guide appropriate antibiotic administration for BSI patients.

Detection of bacterial co-infections and prediction of fatal outcomes in COVID-19 patients presenting to the emergency department using a 29 mRNA host response classifier

Objective

Clinicians in the emergency department (ED) face challenges in concurrently assessing patients with suspected COVID-19 infection, detecting bacterial co-infection, and determining illness severity since current practices require separate workflows. Here we explore the accuracy of the IMX-BVN-3/IMX-SEV-3 29 mRNA host response classifiers in simultaneously detecting SARS-CoV-2 infection, bacterial co-infections, and predicting clinical severity of COVID-19.

Methods

161 patients with PCR-confirmed COVID-19 (52.2% female, median age 50.0 years, 51% hospitalized, 5.6% deaths) were enrolled at the Stanford Hospital ED. RNA was extracted (2.5 mL whole blood in PAXgene Blood RNA) and 29 host mRNAs in response to the infection were quantified using Nanostring nCounter.

Results

The IMX-BVN-3 classifier identified SARS-CoV-2 infection in 151 patients with a sensitivity of 93.8%. Six of 10 patients undetected by the classifier had positive COVID tests more than 9 days prior to enrolment and the remaining oscillated between positive and negative results in subsequent tests. The classifier also predicted that 6 (3.7%) patients had a bacterial co-infection. Clinical adjudication confirmed that 5/6 (83.3%) of the patients had bacterial infections, i.e. Clostridioides difficile colitis (n=1), urinary tract infection (n=1), and clinically diagnosed bacterial infections (n=3) for a specificity of 99.4%. 2/101 (2.8%) patients in the IMX-SEV-3 Low and 7/60 (11.7%) in the Moderate severity classifications died within thirty days of enrollment.

Conclusions

IMX-BVN-3/IMX-SEV-3 classifiers accurately identified patients with COVID-19, bacterial co-infections, and predicted patients’ risk of death. A point-of-care version of these classifiers, under development, could improve ED patient management including more accurate treatment decisions and optimized resource utilization.

Blood Culture Utilization in the Hospital Setting: a Call for Diagnostic Stewardship

There has been significant progress in detection of bloodstream pathogens in recent decades with the development of more sensitive automated blood culture detection systems and the availability of rapid molecular tests for faster organism identification and detection of resistance genes. However, most blood cultures in clinical practice do not grow organisms, suggesting that suboptimal blood culture collection practices (e.g., suboptimal blood volume) or suboptimal selection of patients to culture (i.e., blood cultures ordered for patients with low likelihood of bacteremia) may be occurring. A national blood culture utilization benchmark does not exist, nor do specific guidelines on when blood cultures are appropriate or when blood cultures are of low value and waste resources. Studies evaluating the potential harm associated with excessive blood cultures have focused on blood culture contamination, which has been associated with significant increases in health care costs and negative consequences for patients related to exposure to unnecessary antibiotics and additional testing. Optimizing blood culture performance is important to ensure bloodstream infections (BSIs) are diagnosed while minimizing adverse events from overuse. In this review, we discuss key factors that influence blood culture performance, with a focus on the preanalytical phase, including technical aspects of the blood culture collection process and blood culture indications. We highlight areas for improvement and make recommendations to improve current blood culture practices among hospitalized patients.

Unresolved issues in the epidemiology and diagnosis of bacteremia: an opinion paper

Bacteremia is an important cause of morbidity and mortality worldwide and, despite the diagnostic and therapeutic advances of the last decades, the evidence supporting many diagnostic aspects of bacteremia is scarce. Information on the epidemiological evolution of this entity is limited and many methodological aspects of blood culture collection and analysis are under discussion. Furthermore, the recommendations of the main scientific societies on many of these aspects are variable and, in many cases, have not been updated recently. In this scenario, we have arranged a series of questions on different aspects of bacteremia and reviewed the literature trying to find proper answers for them. We offer our opinion on the topics where the evidence was weak. The topics covered include epidemiological aspects of bacteremia, indications for blood culture extraction, methods for obtaining and incubating samples, or ways of transmitting results from the microbiology laboratory. We do not intend to summarize the current clinical practice guidelines, nor will we deal with the therapeutic management of this entity. The aim of this paper is to review the current perspective on the diagnosis of bacteremia with a critical approach, to point out the gaps in the literature, to offer the opinion of a team dedicated to infectious diseases and clinical microbiology, and to identify some areas of knowledge on which future studies should focus.

Single-site sampling versus multi-site sampling for blood cultures; A retrospective clinical study

Objectives The performance of blood cultures (BC) relies on optimal sampling. Sepsis guidelines do not specify which sampling protocol to use, but recommend two sets of BC bottles, each set containing one aerobic and one anaerobic bottle. For the single-site sampling (SSS) protocol, only one venipuncture is performed for all four bottles. The predominating multi-site sampling (MSS) protocol implies that BC bottles are collected from two separate venipuncture sites. The aim of this study was to compare SSS and MSS. Primary outcomes were number of BC sets collected, sample volume and diagnostic performance. Methods This was a retrospective clinical study comparing BC results in an emergency department before and after changing the sampling protocol to SSS from MSS. All BC samples were incubated in the BacT/ALERT BC system. Results The analysis included 5,248 patients before and 5,364 patients after the implementation of SSS. There was a significantly higher proportion of positive BCs sampled with SSS compared to MSS, 1,049/5,364 (19.56%) and 932/5,248 (17.76%) respectively (P=0.018). This difference was due to a higher proportion of solitary BC sets (two BC bottles) in MSS. Analyzing only patients with the recommended four BC bottles, there was no difference in positivity. SSS had a higher proportion of BC bottles with the recommended sample volumes of 8-12 ml than MSS (P<0.001). Conclusions Changing the sampling protocol to SSS from MSS resulted in higher positivity rates, higher sample volume and fewer solitary BC sets. These advantages of SSS should be considered in future sepsis guidelines.

Mass Spectrometry Proteotyping-Based Detection and Identification of Staphylococcus aureus, Escherichia coli, and Candida albicans in Blood

Bloodstream infections (BSIs), the presence of microorganisms in blood, are potentially serious conditions that can quickly develop into sepsis and life-threatening situations. When assessing proper treatment, rapid diagnosis is the key; besides clinical judgement performed by attending physicians, supporting microbiological tests typically are performed, often requiring microbial isolation and culturing steps, which increases the time required for confirming positive cases of BSI. The additional waiting time forces physicians to prescribe broad-spectrum antibiotics and empirically based treatments, before determining the precise cause of the disease. Thus, alternative and more rapid cultivation-independent methods are needed to improve clinical diagnostics, supporting prompt and accurate treatment and reducing the development of antibiotic resistance. In this study, a culture-independent workflow for pathogen detection and identification in blood samples was developed, using peptide biomarkers and applying bottom-up proteomics analyses, i.e., so-called "proteotyping". To demonstrate the feasibility of detection of blood infectious pathogens, using proteotyping, Escherichia coli and Staphylococcus aureus were included in the study, as the most prominent bacterial causes of bacteremia and sepsis, as well as Candida albicans, one of the most prominent causes of fungemia. Model systems including spiked negative blood samples, as well as positive blood cultures, without further culturing steps, were investigated. Furthermore, an experiment designed to determine the incubation time needed for correct identification of the infectious pathogens in blood cultures was performed. The results for the spiked negative blood samples showed that proteotyping was 100- to 1,000-fold more sensitive, in comparison with the MALDI-TOF MS-based approach. Furthermore, in the analyses of ten positive blood cultures each of E. coli and S. aureus, both the MALDI-TOF MS-based and proteotyping approaches were successful in the identification of E. coli, although only proteotyping could identify S. aureus correctly in all samples. Compared with the MALDI-TOF MS-based approaches, shotgun proteotyping demonstrated higher sensitivity and accuracy, and required significantly shorter incubation time before detection and identification of the correct pathogen could be accomplished.

Comparison of Microorganism Detection and Time to Positivity in Pediatric and Standard Media from Three Major Commercial Continuously Monitored Blood Culture Systems

New blood culture instrumentation and medium formulations have led to improved time to positivity (TTP) for positive blood cultures. Data regarding the necessity of pediatric blood culture bottles with contemporary blood culture systems are sparse. We compared performance of three commercial blood culture systems, evaluating impact of blood volumes in standard and pediatric blood culture media across systems. Simulated blood cultures with packed red blood cells (PRBCs) and three Gram-positive, four Gram-negative, and one anaerobic organism (final concentrations ranging from 0.5 to 19 CFU/ml blood) on the Virtuo, VersaTrek, and Bactec FX instruments were evaluated with FAN Plus, Redox, and Bactec Plus media, respectively. For each medium/instrument/organism combination, 1-, 3-, 5-, and 10-ml blood volumes were evaluated in triplicate. Detection rate was not affected by blood volume. Aerobic organisms that demonstrated variable rates of detection were Kingella kingae, Haemophilus influenzae, and Neisseria meningitidis. Bacteroides fragilis was detected in 83%, 100%, and 100% of Virtuo, VersaTrek, and Bactec anaerobic bottles, respectively. The average TTP of standard medium for aerobic organisms detected on Virtuo was decreased compared to those for VersaTrek (-2.3 h) and Bactec (-4.9 h). Compared to standard medium, detection rate and TTP were unchanged on Virtuo, while TTP was reduced with pediatric medium for 2/8 organisms tested on Bactec and 7/8 organisms on VersaTrek, illustrating the potential benefit of pediatric medium on VersaTrek or Bactec when low blood volumes (<5 ml) are collected. These results demonstrate that TTP is decreased on the Virtuo compared to VersaTrek and Bactec for many microorganisms associated with bloodstream infection (BSI) but may have species-specific limitations.

Effective and Rapid Microbial Identification in Pediatric Osteoarticular Infections Using Blood Culture Bottles

BACKGROUND

The detection and identification of pathogenic microorganisms are essential for the treatment of osteoarticular infection. However, obtaining a sufficient amount of specimen from pediatric patients is often difficult. Herein, we aimed to demonstrate the effectiveness of the blood culture bottle (BCB) system in pediatric osteoarticular infections. We hypothesized that our BCB culture method is superior to the conventional swab and tissue culture methods in terms of required specimen size, incubation time, and microbial identification rate.

METHODS

We analyzed the prospectively collected data of pediatric patients who underwent surgical treatment for osteoarticular infections between August 2016 and October 2019. Four needles were dipped in the infected fluid or tissue during the surgical procedure as soon as the infected area was exposed and were used to inoculate 2 aerobic pediatric BCBs and 2 anaerobic general BCBs. We also collected 2 conventional swab samples and 2 tissue samples from the identical area. The microbial identification rate and the time required for identification were compared between BCB, swab, and tissue cultures.

RESULTS

Forty patients constituted the study group; 13 patients had osteomyelitis, 17 patients had septic arthritis, and 10 patients had both. Of these 40 patients, the microbial identification rate was higher with BCB cultures (27 [68%]) than with swab cultures (18 [45%]; p = 0.004) or tissue cultures (15 [38%]; p < 0.001). Nine samples (9 patients [23%]) were only positive in the BCB culture. Positive microbial growth was not detected with conventional culture methods when microorganisms did not grow on the BCB culture. Compared with swab culture (4.3 ± 1.1 days; p < 0.001) or tissue culture (4.4 ± 1.1 days; p < 0.001), the BCB culture reduced the time required for microbial identification (3.5 ± 0.9 days).

CONCLUSIONS

In pediatric osteoarticular infections, the BCB culture system improved the microbial identification rate, reduced the time to identification, and permitted a smaller-volume specimen, compared with traditional culture systems.

LEVEL OF EVIDENCE

Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Time for pragmatic, prospective clinical trials to determine the role of empirical antibacterial therapy in critically ill adults hospitalized with malaria

BACKGROUND

Children with severe falciparum malaria in malaria-endemic regions are predisposed to developing life-threatening bacterial co-infection. International guidelines therefore recommend empirical broad-spectrum antibacterial therapy in these children. Few studies have examined co-infection in adults, although it has been believed to be relatively rare; antibacterial therapy is therefore not routinely recommended in adults with falciparum malaria.

DISCUSSION

However, the fundamental pathophysiology of falciparum malaria in adults and children is the same; it is therefore unclear why adults would not also be predisposed to bacterial infection. Indeed, recent studies have identified bacteraemia in >10% of adults hospitalized with malaria. Some have suggested that these adults probably had bacterial sepsis, with the parasitaemia an incidental finding. However, it is usually impossible in resource-limited settings to determine-at presentation-whether critically ill, parasitaemic adults have severe malaria, bacterial sepsis, or both. Given the significant case-fatality rates of severe malaria and bacterial sepsis, the pragmatic initial approach would be to cover both possibilities.

CONCLUSIONS

Life-threatening bacterial co-infection may be more common in critically ill adults with malaria than previously believed. While further prospective data are awaited to confirm these findings, it might be more appropriate to provide empirical aantibacterial cover in these patients than current guidelines suggest.

Single-Sampling Strategy vs. Multi-Sampling Strategy for Blood Cultures in Sepsis: A Prospective Non-inferiority Study

Background

Optimal sampling is critical for the performance of blood cultures (BCs). Most guidelines recommend collecting 40 ml of blood, divided between two venipuncture sites, i.e., multi-sampling strategy (MSS). Sampling through a single venipuncture site, i.e., single-sampling strategy (SSS) is easier; however, the diagnostic performance of SSS compared to MSS remains unknown. Thus, we aimed to study if SSS is non-inferior to MSS for detection of pathogenic microorganisms.

Methods

A prospective, paired, non-inferiority design was used. Patients with clinically suspected sepsis admitted to an Emergency Department were included. Six BC bottles were simultaneously collected, consisting of four BC bottles from the first arm and two from the other arm. SSS consisted of BC bottles 1, 2, 3, and 4, and MSS consisted of BC bottles 1, 2, 5, and 6. Samples were incubated in a BacT/ALERT BC system.

Results

The final analysis included 549 episodes. Pathogenic microorganisms were detected in 162 cases (29.5%) with MSS and 160 cases (29.1%) with SSS, yielding an absolute difference of 0.36%, with a 95% confidence interval of -1.33 to 2.06%, which did not exceed the predefined non-inferiority margin of 5%. MSS tended to produce more contaminant growth (7.3% of cases) than SSS (5.3% of cases; p = 0.072).

Conclusion

The study showed that SSS was non-inferior to MSS in detecting pathogenic microorganisms and supports the use of SSS as a routine method.

Digital microbiology

BACKGROUND

Digitalization and artificial intelligence have an important impact on the way microbiology laboratories will work in the near future. Opportunities and challenges lie ahead to digitalize the microbiological workflows. Making efficient use of big data, machine learning, and artificial intelligence in clinical microbiology requires a profound understanding of data handling aspects.

OBJECTIVE

This review article summarizes the most important concepts of digital microbiology. The article gives microbiologists, clinicians and data scientists a viewpoint and practical examples along the diagnostic process.

SOURCES

We used peer-reviewed literature identified by a PubMed search for digitalization, machine learning, artificial intelligence and microbiology.

CONTENT

We describe the opportunities and challenges of digitalization in microbiological diagnostic processes with various examples. We also provide in this context key aspects of data structure and interoperability, as well as legal aspects. Finally, we outline the way for applications in a modern microbiology laboratory.

IMPLICATIONS

We predict that digitalization and the usage of machine learning will have a profound impact on the daily routine of laboratory staff. Along the analytical process, the most important steps should be identified, where digital technologies can be applied and provide a benefit. The education of all staff involved should be adapted to prepare for the advances in digital microbiology.