Field trials of blood culture identification FilmArray in regional Australian hospitals

Performance of molecular tests for diagnosis of bloodstream infections in the clinical setting: a systematic literature review and meta-analysis

BACKGROUND

Rapid identification of bloodstream pathogens and associated antimicrobial resistance (AMR) profiles by molecular tests from positive blood cultures (PBCs) have the potential to improve patient management and clinical outcomes.

OBJECTIVES

A systematic review and meta-analysis were conducted to evaluate diagnostic test accuracy (DTA) of molecular tests from PBCs for detecting pathogens and AMR in the clinical setting.

METHODS

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DATA SOURCES

Medline, Embase, Cochrane, conference proceedings, and study bibliographies were searched.

STUDY ELIGIBILITY CRITERIA

Studies evaluating DTA of commercially available molecular tests vs. traditional phenotypic identification and susceptibility testing methods in patients with PBCs were eligible.

PARTICIPANTS

Patients with PBCs.

TESTS

Commercially available molecular tests.

REFERENCE STANDARD

Traditional phenotypic identification and susceptibility testing methods (standard of care, SOC).

ASSESSMENT OF RISK OF BIAS

Study quality was assessed using Quality Assessment of Diagnostic Accuracy Studies-2.

METHODS OF DATA SYNTHESIS

Summary DTA outcomes were estimated using bivariate random-effects models for gram-negative bacteria (GNB), gram-positive bacteria (GPB), yeast, GNB-AMR, GPB-AMR, and specific targets when reported by ≥ 2 studies (PROSPERO CRD42023488057).

RESULTS

Seventy-four studies including 24 590 samples were analysed, most of which had a low risk of bias. When compared with SOC, molecular tests showed 92-99% sensitivity, 99-100% specificity, 99-100% positive predictive value, and 97-100% negative predictive value for identifying total GNB (43 studies), GPB (38 studies), yeast (24 studies), GNB-AMR (35 studies), and GPB-AMR (39 studies). For individual pathogen targets, 93-100% sensitivity, 98-100% specificity, 86-100% positive predictive value, and 99-100% negative predictive value were estimated. Five of seven AMR genes had 91-99% sensitivity and 99-100% specificity. Sensitivity was lower for IMP (four studies; 62%; 95% CI, 34-83%) and VIM (four studies; 70%; 95% CI, 38-90%) carbapenemases, where genes were not detected or were not harboured in Pseudomonas aeruginosa (i.e. low prevalence). Performance of molecular tests in detecting AMR was generally comparable when grouped by geographical region (Europe, North America, and East Asia).

DISCUSSION

High DTA support the use of molecular tests in identifying a broad panel of pathogens and detecting AMR in GNB and GPB.

Impact of Introducing a Multiplex Polymerase Chain Reaction Blood Culture Panel on Anti-Methicillin-Resistant Staphylococcus aureus (MRSA) and Carbapenem Antimicrobial Agents in a Children's Hospital

BACKGROUND

With the advent of multiplex polymerase chain reaction (PCR) using samples from a positive blood culture, the time required to identify a pathogen has significantly shortened to a few hours. It can help us select appropriate antimicrobial agents more quickly. The present study aimed to assess the impact of using a multiplex PCR blood culture panel on the appropriate administration of antimicrobial agents.

METHODS

Patients aged <16 years with culture-confirmed bacteremia at Tokyo Metropolitan Children's Medical Center were enrolled. A pre-intervention period (period I: December 2016 to December 2018) and a post-intervention period with multiplex PCR use for the confirmation of positive blood cultures (period II: December 2019 to December 2021) were compared for their effect on the use of antimicrobial agents for gram-positive cocci (GPC) and gram-negative rod (GNR) bacteremia. Data on patient background, blood culture results, and antimicrobial use were retrospectively collected from electronic medical records.

RESULTS

Periods I and II had 174 and 154 patients, respectively. The median age at periods I and II was 14 (IQR 2-82) months and 12 (IQR 1-78) months, respectively. GPC bacteremia during periods I and II occurred in 140 and 115 patients, respectively. GNR during periods I and II occurred in 34 and 39 patients, respectively. Neither the vancomycin-resistance genes A/B nor the carbapenem-resistance gene were detected. The use of antimicrobial agents against anti-methicillin-resistant Staphylococcus aureus (MRSA) for GPC bacteremia decreased from 103/140 cases (73%) in period I to 56/115 cases (49%) in period II (p=0.047). The use of carbapenems for GNR bacteremia did not change significantly, at 23/34 (68%) in period I and 34/39 (87%) in period II (p=0.47).

CONCLUSION

Introducing multiplex PCR for pediatric bacteremia decreased the use of anti-MRSA antimicrobial agents but not of carbapenems.

Blood culture identification (BCID) performance in polymicrobial bacteremia

The rapid multiplex PCR (rmPCR)-based FilmArray® blood culture identification (BCID) assay reduces time from positive blood culture to organism identification. Polymicrobial bacteremia (PMB) is a known area of reduced diagnostic fidelity for BCID and remains incompletely characterized. All cases of clinically confirmed PMB at a large academic single center from a 23-month period were evaluated in a retrospective cohort analysis. A total of 207 samples were identified and studied. Overall, 49.3% (N = 102) of polymicrobial cultures were incompletely identified by FilmArray® result. There were no significant between-group differences in comorbidity status, length of stay, mortality, or source between patients with PMB who had complete versus incomplete BCID identification. Our results suggest that rmPCR-based assays frequently miss organisms in PMB and should be interpreted accordingly.

Speaking of sepsis: semantics, syntax, and slang

Medical language is in a constant state of evolution. Its grammar and vocabulary are not fixed by rigid rules. The interdisciplinary field of sepsis has become a meeting point for new insights arising from advances in systems biology, epidemiology, mechanistic understandings of disease process and antimicrobial interventions. This convergence has gained from our recent experience of SARS-CoV-2 infection and COVID-19 and possibilities inferred from emerging information technology. Biomedical descriptors have diverged along disciplinary lines creating an unfortunate disconnect between clinical and laboratory-based terminology. The resulting confusion between clinically determined sepsis and laboratory verified bloodstream infection raises practical questions that affect daily operational processes in the ward, clinic and laboratory. There is an urgent need to understand how the clinical sepsis pathway and corresponding clinical laboratory workflow can be better aligned as a single coherent entity. There is also an implicit need to understand how this process should produce actionable information in a timely and orderly manner, and identify residual obselete terminology that has crept into common usage. A widely accepted sepsis epistemology, ontology and heuristic will help us improve our clinical management of sepsis.

Diagnostic efficiency of the FilmArray blood culture identification (BCID) panel: a systematic review and meta-analysis

Introduction. The FilmArray blood culture identification panel (BCID) panel is a multiplex PCR assay with high sensitivity and specificity to identify the most common pathogens in bloodstream infections (BSIs).Hypothesis. We hypothesize that the BCID panel has good diagnostic performance for BSIs and can be popularized in clinical application.Aim: To provide summarized evidence for the diagnostic accuracy of the BCID panel for the identification of positive blood cultures.Methodology. We searched the MEDLINE, EMBASE and Cochrane databases through March 2021 and assessed the efficacy of the diagnostic test of the BCID panel. We performed a meta-analysis and calculated the summary sensitivity and specificity of the BCID panel. Systematic review protocols were registered in the International Prospective Register of Systematic Reviews (PROSPERO) (registration number CRD42021239176).Results. A total of 16 full-text articles were eligible for analysis. The overall sensitivities of the BCID panel on Gram-positive bacteria, Gram-negative bacteria and fungi were 97 % (95 % CI, 0.96-0.98), 100 % (95 % CI, 0.98-01.00) and 99 % (95 % CI, 0.87-1.00), respectively. The pooled diagnostic specificities were 99 % (95 % CI, 0.97-1.00), 100 % (95 % CI, 1.00-1.00) and 100 % (95 % CI, 1.00-1.00) for Gram-positive bacteria, Gram-negative bacteria and fungi, respectively.Conclusions. The BCID panel has high rule-in value for the early detection of BSI patients. The BCID panel can still provide valuable information for ruling out bacteremia or fungemia in populations with low pretest probability.

Molecular Methodologies for Improved Polymicrobial Sepsis Diagnosis

Polymicrobial sepsis is associated with worse patient outcomes than monomicrobial sepsis. Routinely used culture-dependent microbiological diagnostic techniques have low sensitivity, often leading to missed identification of all causative organisms. To overcome these limitations, culture-independent methods incorporating advanced molecular technologies have recently been explored. However, contamination, assay inhibition and interference from host DNA are issues that must be addressed before these methods can be relied on for routine clinical use. While the host component of the complex sepsis host–pathogen interplay is well described, less is known about the pathogen’s role, including pathogen–pathogen interactions in polymicrobial sepsis. This review highlights the clinical significance of polymicrobial sepsis and addresses how promising alternative molecular microbiology methods can be improved to detect polymicrobial infections. It also discusses how the application of shotgun metagenomics can be used to uncover pathogen/pathogen interactions in polymicrobial sepsis cases and their potential role in the clinical course of this condition.

Development, deployment and in-field demonstration of mobile coronavirus SARS-CoV-2 Nucleic acid amplification test

Introduction. The evolving SARS-CoV-2 coronavirus pandemic presents a series of challenges to clinical diagnostic services. Many proprietary PCR platforms deployed outside centralised laboratories have limited capacity to upscale when public health demands increase. We set out to develop and validate an open-platform mobile laboratory for remote area COVID-19 diagnosis, with a subsequent field trial.Gap Statement. In regional Western Australia, molecular diagnostic support is limited to near point-of-care devices. We therefore aimed to demonstrate open-platform capability in a rapidly deployable format within the context of the COVID-19 pandemic.Methodology. We compared, selected and validated components of a SARS-CoV-2 RT-PCR assay in order to establish a portable molecular diagnostics laboratory. The optimal combination of PCR assay equipment, reagents and consumables required for operation to national standards in regional laboratories was identified. This comprised RNA extraction and purification (QuickGene-480, Kurabo, Japan), a duplex RT-PCR assay (Logix Smart COVID-19, Co-Diagnostics, USA), a Myra liquid handling robot (Biomolecular Systems, Australia) and a magnetic induction thermal cycler (MIC, Biomolecular Systems).Results The 95 and 99% limits of detection were 1.01 copies μl-1 (5.05 copies per reaction) and 2.80 copies μl-1 (14.00 copies per reaction) respectively. The Co-Diagnostics assay amplified both SARS-CoV-1 and -2 RNA but showed no other cross reactivity. Qualitative results aligned with the reference laboratory SARS-CoV-2 assay (sensitivity 100% [95 % CI 96.48-100%], specificity 100% [95% CI 96.52-100%]). In field trials, the laboratory was operational within an hour of arrival on-site, can process up to 36 samples simultaneously, produces results in two and a half hours from specimen reception, and performed well during six consecutive runs during a 1 week deployment.Conclusion. Our mobile laboratory enables an adaptive response to increased test demand, and unlike many proprietary point-of-care PCR systems, rapid substitution with an alternative assay if gene targets change or reagent supply chains fail. We envisage operation of this RT-PCR assay as a standby capability to meet varying regional test demands under public health emergency operations guidance.

Rapid antimicrobial susceptibility tests for sepsis; the road ahead

Current methods for antimicrobial susceptibility testing (AST) are too slow to affect initial treatment decisions in the early stages of sepsis, when the prescriber is most concerned to select effective therapy immediately, rather than finding out what will not work 1 or 2 days later. There is a clear need for much faster differentiation between viral and bacterial infection, and AST, linked to earlier aetiological diagnosis, without sacrificing either the accuracy of quantitative AST or the low cost of qualitative AST. Truly rapid AST methods are eagerly awaited, and there are several candidate technologies that aim to improve the targeting of our limited stock of effective antimicrobial agents. However, none of these technologies are approaching the point of care and nor can they be described as truly culture-independent diagnostic tests. Rapid chemical and genomic methods of resistance detection are not yet reliable predictors of antimicrobial susceptibility and often rely on prior bacterial isolation. In order to resolve the trade-off between diagnostic confidence and therapeutic efficacy in increasingly antimicrobial-resistant sepsis, we propose a series of three linked decision milestones: initial clinical assessment (e.g. qSOFA score) within 10 min, initial laboratory tests and presumptive antimicrobial therapy within 1 h, and definitive AST with corresponding antimicrobial amendment within an 8 h window (i.e. the same working day). Truly rapid AST methods therefore must be integrated into the clinical laboratory workflow to ensure maximum impact on clinical outcomes of sepsis, and diagnostic and antimicrobial stewardship. The requisite series of development stages come with a substantial regulatory burden that hinders the translation of innovation into practice. The regulatory hurdles for the adoption of rapid AST technology emphasize technical accuracy, but progress will also rely on the effect rapid AST has on prescribing behaviour by physicians managing the care of patients with sepsis. Early adopters in well-equipped teaching centres in close proximity to large clinical laboratories are likely to be early beneficiaries of rapid AST, while simplified and lower-cost technology is needed to support poorly resourced hospitals in developing countries, with their higher burden of AMR. If we really want the clinical laboratory to deliver a specific, same-day diagnosis underpinned by definitive AST results, we are going to have to advocate more effectively for the clinical benefits of bacterial detection and susceptibility testing at critical decision points in the sepsis management pathway.