Impact of Xpert MRSA/SA blood culture PCR assay on management of positive blood cultures in obstetric patients: a retrospective audit

Optimizing Treatment of Staphylococcus aureus Bloodstream Infections Following Rapid Molecular Diagnostic Testing and an Antimicrobial Stewardship Program Intervention

Pending antibiotic susceptibility results, vancomycin is often used for bloodstream infections (BSIs) to ensure treatment of methicillin-resistant Staphylococcus aureus (MRSA). As rapid discrimination of methicillin-susceptible S. aureus (MSSA) from MRSA in BSIs could decrease vancomycin use and allow early optimization of beta-lactam therapy, this study evaluated the impact of the use of rapid molecular testing for MSSA and MRSA coupled with an antimicrobial stewardship program (ASP) intervention. Between January and July 2020, the Cepheid Xpert MRSA/SA blood culture assay was performed on blood cultures with Gram-positive cocci in clusters that were identified as S. aureus using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The ASP team member then consulted with the treating physician. The time to optimal therapy (TTOT) and clinical outcomes, including length of hospital stay (LOS), were compared between the intervention (n = 29) and historical (n = 27) cohorts. TTOT was defined as the time from the first blood culture draw to the use of appropriately dosed antistaphylococcal beta-lactam monotherapy without vancomycin. Molecular testing significantly reduced the median time to MSSA and MRSA discrimination to 7.8 h, compared to 24.3 h with culture-based methods (P < 0.001). Compared to the control group, the median TTOT in the ASP intervention group was significantly shorter (P = 0.041) at 38.0 h (versus 50.1 h). Rapid discrimination between MRSA and MSSA using molecular testing, paired with an ASP intervention, significantly reduced the TTOT in patients with MSSA BSIs. IMPORTANCE Our research shows that time to optimal antibiotic treatment for serious bloodstream infections can be improved with rapid molecular sensitivity testing and feedback to prescribers. This can be implemented in laboratories without full microbiology services or training to improve patient outcomes by improving antimicrobial use.

Clinical Relevance of Xpert MRSA/SA in Guiding Therapeutic Decisions for Staphylococcal Infections: A Diagnostic Test Accuracy Analysis

Introduction

Rapid identification of the causal organism and antibiotic resistance is crucial for guiding targeted therapy in patients with suspected staphylococcal infection. A meta-analysis was carried out to evaluate the diagnostic relevance of Xpert™ MRSA/SA (Xpert) from clinical samples of various origins for limiting the use of unnecessary empirical methicillin-resistant Staphylococcus aureus (MRSA) therapy.

Methods

Five databases, including the Cochrane Library, Scopus, PubMed, Web of Science, and Embase, were comprehensively inspected from inception to October 12, 2021. The pooled summary estimates were evaluated using a bivariate random-effects model.

Results

Our inclusion criteria were met by 49 publications containing 68 datasets out of 735 citations. A total of 21 studies (n = 4996) examined the accuracy of Xpert in detecting methicillin-sensitive S. aureus (MSSA), while 47 studies (n = 45,430) examined the accuracy of Xpert in detecting MRSA. As compared to MRSA, Xpert’s diagnostic performance for MSSA detection was markedly higher [sensitivity: 0.97 (0.96–0.98), specificity: 0.97 (0.97–0.98), area under curve (AUC): 0.99 (0.99–1.0)]. Xpert’s pooled sensitivity and specificity differed marginally across sample types, including screening of colonization, lower respiratory tract (LRT), osteoarticular, and bloodstream samples. Notably, the Xpert pooled specificity was consistently ≥ 92% against microbiological culture across all sample types. The diagnostic efficiency heterogeneity was not explained by a meta-regression and subgroup analysis of research design, sample conditions, and sampling methods (P > 0.05).

Conclusion

Our findings suggest that Xpert could be used as the favoured screening test for the early detection of staphylococcal infection in a variety of sample types, with the goal of guiding therapeutic decisions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40121-022-00632-w.

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.

Rapid Detection of PBP2a in Staphylococci from Shortly Incubated Subcultures of Positive Blood Cultures by an Immunochromatographic Assay

Staphylococcus aureus, as well as coagulase-negative staphylococci (CoNS), can cause a wide range of human infections both in nosocomial and community settings. Βeta-lactams are the antibiotics of choice for the treatment of bloodstream infections (BSI) caused by these microorganisms. Resistance to virtually all β-lactams (also referred to as methicillin resistance) primarily results from the production of an alternative penicillin-binding protein (PBP2a) encoded by the mecA gene. While β-lactams are still used as first-line therapy against BSI caused by S. aureus, BSI with CoNS are usually treated with vancomycin due to the high prevalence of methicillin resistance. Rapid detection of methicillin resistance is thus critical for continuation or adjustment of the empirical therapy and therewith to improve the clinical outcome of the patients. The revised version of the immunochromatographic assay PBP2a SA culture colony test (SACCT) is a rapid, inexpensive, and easy method that enables reliable detection of PBP2a in mecA-positive staphylococcal isolates after18 to 24 h of incubation. Here, we evaluated the diagnostic performance of the SACCT using primary subcultures of spiked blood cultures after short incubation (4 to 6 h) and established a modified procedure with an equal analytical performance to that of longer-grown cultures. With the proposed method the SACCT can be employed for PBP2a detection from shortly incubated subcultures of clinically relevant staphylococcal isolates, thereby allowing more rapid and effective management of BSI caused by these organisms.

IMPORTANCE Antibiotic resistance poses a major threat to health and incurs high economic costs worldwide. Rapid detection of resistance mechanisms can contribute to improving patient care and preventing the dissemination of antimicrobial resistance. Here, we describe a rapid method to detect the most important beta-lactam resistance mechanism (the plasmid-encoded alternative transpeptidase PBP2a) in staphylococcal isolates causing BSI. We show that, using a modified procedure, PBP2a can be reliably detected from primary subcultures of spiked blood cultures after short incubation (4 to 6 h) with a rapid, inexpensive, and simple immunochromatographic test (SACCT). We provide an accurate, inexpensive, and rapid method to facilitate appropriate management and control of infections in patients suffering from invasive staphylococcal infections.

Clinical impact of implementation of rapid diagnostic testing of blood cultures with Staphylococcus aureus on patient outcomes

Rapid diagnostic testing in microbiology labs shortens the time to identification of bacteria in blood cultures. Cepheid® GeneXpert® MRSA/SA PCR can be used to distinguish MRSA and MSSA from non-Staphylococcus aureus organisms in blood cultures. This study aims to determine if implementation of MRSA/SA PCR for blood culture pathogen identification, plus daily antimicrobial stewardship intervention, can reduce time to appropriate therapy, vancomycin duration, 30 day mortality, and 90 day recurrence in veterans. A total of 113 patients in the pre-implementation cohort and 73 patients in the post-implementation cohort were evaluated. Time to appropriate therapy was decreased from 49.8 (pre-implementation) to 20.6 (post-implementation) hours. There was a numerically shorter median duration of vancomycin therapy in the post-implementation group. There was no difference in 30 day mortality or 90 day recurrence between groups. Use of MRSA/SA PCR can improve antimicrobial use when combined with once-daily antimicrobial stewardship review.

Advances in rapid diagnostics for bloodstream infections

Septicemia from bloodstream infections (BSI) is the second largest cause of inpatient mortality and the single most expensive condition for US hospitals to manage. There has been an explosive development of commercial diagnostic systems to accelerate the identification and antimicrobial susceptibility testing (AST) of causative pathogens. Despite adoption of advanced technologies like matrix-assisted laser desorption imaging-time-of-flight mass spectrometry and multiplex polymerase chain reaction for rapid identification, clinical impact has been variable, in part due to the persistent need for conventional AST as well as prescriber understanding of these rapidly evolving platforms. Newer technologies are expanding on rapid detection of genotypic determinants of resistance, but only recently has rapid phenotypic AST been available. Yet, improved outcomes with rapid diagnostic platforms are still most evident in conjunction with active antimicrobial stewardship. This review will outline key advancements in rapid diagnostics for BSI and the role of antimicrobial stewardship in this new era.

Prediction of methicillin-resistant Staphylococcus aureus bloodstream infection: do we need rapid diagnostic tests?

Staphylococcus aureus (SA) is the leading cause of bloodstream infection (BSI). The incidence of methicillin-resistant SA (MRSA) has decreased in France and Europe since one decade. Early and precise prediction of methicillin susceptibility is needed to improve probabilistic antibiotic therapy of MRSA-BSI. The aim of this study was to identify MRSA-BSI risk factors at admission and evaluate which patients need costly rapid diagnostic tests. A single-center retrospective descriptive study of all diagnosed SA-BSI was conducted in a French University Hospital between January 2015 and December 2016. All medical charts were reviewed. Univariate and multivariate analyses by a logistic regression model were performed on the data. We then build a prediction score of MRSA-BSI by assigning one point for each of the risk factor identified. During the study period, 151 SA-BSI were identified including 32 (21%) MRSA-BSI. In multivariate analysis, three factors were associated with MRSA-BSI: coming from long-term care facility, known previous MRSA colonization and/or infection, and chronic renal disease. Among our population, respectively, 5% and 100% had a MRSA-BSI when no or three risk factors were identified. Therefore, among the PCR performed, 43 (96%) could be avoided according to our clinical score. In our study, methicillin-susceptible SA and MRSA-BSI can be predictable by counting MRSA risk factors. This prediction rule could avoid the use of expensive rapid diagnostic tests. Prospective studies and prediction rules could help physicians to predict SA-BSI susceptibility to improve appropriate empiric therapy choice.

Impact of MRSA on the Military Medical Service and Diagnostic Point-of-Care Options for the Field Setting

Methicillin-resistant Staphylococcus aureus (MRSA) poses an infection risk for international military deployments. In the presented mini-review, the history of MRSA in the medical service and modern warfare is highlighted. To allow rapid diagnosis, various molecular diagnostic point-of-care solutions are available. Most evaluation studies, however, are focused on screening swabs rather than clinical materials and evaluation data from harsh environments are widely lacking. Accordingly, studies with complex sample materials under difficult environmental conditions, e.g., in the desert or in the tropics, are desirable to close this gap of knowledge regarding the diagnostic reliability of such modern molecular point-of-care devices.

Recent advances in the microbiological diagnosis of bloodstream infections

Rapid identification (ID) and antimicrobial susceptibility testing (AST) of the causative agent(s) of bloodstream infections (BSIs) are essential for the prompt administration of an effective antimicrobial therapy, which can result in clinical and financial benefits. Immediately after blood sampling, empirical antimicrobial therapy, chosen on clinical and epidemiological data, is administered. When ID and AST results are available, the clinician decides whether to continue or streamline the antimicrobial therapy, based on the results of the in vitro antimicrobial susceptibility profile of the pathogen. The aim of the present study is to review and discuss the experimental data, advantages, and drawbacks of recently developed technological advances of culture-based and molecular methods for the diagnosis of BSI (including mass spectrometry, magnetic resonance, PCR-based methods, direct inoculation methods, and peptide nucleic acid fluorescence in situ hybridization), the understanding of which could provide new perspectives to improve and fasten the diagnosis and treatment of septic patients. Although blood culture remains the gold standard to diagnose BSIs, newly developed methods can significantly shorten the turnaround time of reliable microbial ID and AST, thus substantially improving the diagnostic yield.