Clinical outcomes with rapid detection of methicillin-resistant and methicillin-susceptible Staphylococcus aureus isolates from routine blood cultures

Rapid versus standard antimicrobial susceptibility testing to guide treatment of bloodstream infection

BACKGROUND

Rapid antimicrobial susceptibility tests are expected to reduce the time to clinically important results of a blood culture. This might enable clinicians to better target therapy to a person's needs, and thereby, improve health outcomes (mortality, length of hospital stay), and reduce unnecessary prescribing of broad-spectrum antibiotics; thereby reducing antimicrobial resistance rates.

OBJECTIVES

To assess the effects of rapid susceptibility testing versus standard susceptibility testing for bloodstream infections (BSIs).

SEARCH METHODS

To identify studies with selected outcomes, we searched the Cochrane Infectious Diseases Group Specialised Register, CENTRAL, MEDLINE, LILACS, and two trials registries, between 1987 and October 2020. We used 'bloodstream infection' and 'antimicrobial susceptibility tests' as search terms. We had no language or publication status limitations.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing rapid antimicrobial susceptibility testing (with a time-to-result of ≤ 8 hours) versus conventional antimicrobial susceptibility testing in people with a BSI caused by any bacteria, as identified by a positive blood culture.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened references, full-text reports of potentially relevant studies, extracted data from the studies, and assessed risk of bias. Any disagreement was discussed and resolved with a third review author. For mortality, a dichotomous outcome, we extracted the number of events in each arm, and presented a risk ratio (RR) with 95% confidence interval (CI) to compare rapid susceptibility testing to conventional methods. We used Review Manager 5.4 to meta-analyse the data. For other outcomes, which are time-to-event outcomes (time-to-discharge from hospital, time-to-first appropriate antibiotic change), we conducted qualitative narrative synthesis, due to heterogeneity of outcome measures.  MAIN RESULTS: We included six trials, with 1638 participants. For rapid antimicrobial susceptibility testing compared to conventional methods, there was little or no difference in mortality between groups (RR 1.10, 95% CI 0.82 to 1.46; 6 RCTs, 1638 participants; low-certainty evidence). In subgroup analysis, for rapid genotypic or molecular antimicrobial susceptibility testing compared to conventional methods, there was little or no difference in mortality between groups (RR 1.02, 95% CI 0.69 to 1.49; 4 RCTs, 1074 participants; low-certainty evidence). For phenotypic rapid susceptibility testing compared to conventional methods, there was little or no difference in mortality between groups  (RR 1.37, 95% CI 0.80 to 2.35; 2 RCTs, 564 participants; low-certainty evidence). In qualitative analysis, rapid susceptibility testing may make little or no difference in time-to-discharge (4 RCTs, 1165 participants; low-certainty evidence). In qualitative analysis, rapid genotypic susceptibility testing compared to conventional testing may make little or no difference in time-to-appropriate antibiotic (3 RCTs, 929 participants; low-certainty evidence). In subgroup analysis, rapid phenotypic susceptibility testing compared to conventional testing may improve time-to-appropriate antibiotic (RR -17.29, CI -45.05 to 10.47; 2 RCTs, 564 participants; low-certainty evidence).  AUTHORS' CONCLUSIONS: The theoretical benefits of rapid susceptibility testing have not been demonstrated to directly improve mortality, time-to-discharge, or time-to-appropriate antibiotic in these randomized studies. Future large prospective studies should be designed to focus on the most clinically meaningful outcomes, and aim to optimize blood culture pathways.

[Evaluation of a rapid assay for detection of PBP2a Staphylococcus aureus]

OBJECTIVE

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen causing both healthcare-associated and community-acquired infection. Rapid and accurate detection of this pathogen is crucial for the use of appropriate antimicrobial therapy and the control of nosocomial spread.

METHODS

A total of 107 S. aureus strains were assayed for methicillin resistance: Vitek2® (bioMérieux), CHROMagarTM MRSA II (BD Becton Dickinson), disk diffusion in agar for cefoxitin 30 μg and immunochromatography PBP2a SA Culture Colony Test (AlereTM). The results of conventional tests were compared with the "gold standard" PCR test for mecA gene.

RESULTS

Sensitivity and specificity were: disk diffusion for cefoxitin 100% and 100% respectively, Vitek2® 100 and 100%, CHROMagarTM MRSA II 100 and 96%, and ICPBP2a detection 98,25% and 100%.

CONCLUSIONS

ICPBP2a Culture Colony Test (AlereTM) is fast, efficient and economical technique for detection of penicillin binding protein 2a (PBP2a) from isolates. This assay is a useful tool for the management of hospital outbreaks.

Role of the Clinical Microbiology Laboratory in Antimicrobial Stewardship

For adequate antimicrobial stewardship, microbiology needs to move from the laboratory to become physically and verbally amenable to the caregivers of an institution. Herein, we describe the contributions of our microbiology department to the antimicrobial stewardship program of a large teaching hospital as 10 main points ranging from the selection of patients deemed likely to benefit from a fast track approach, to their clinical samples, or the rapid reporting of results via a microbiology hotline, to rapid searches for pathogens and susceptibility testing. These points should serve as guidelines for similar programs designed to decrease the unnecessary use of antimicrobials.

Collaboration between an antimicrobial stewardship team and the microbiology laboratory can shorten time to directed antibiotic therapy for methicillin-susceptible staphylococcal bacteremia and to discontinuation of antibiotics for coagulase-negative staphylococcal contaminants

BACKGROUND

Rapid identification of Gram-positive cocci in clusters (GPCC) in positive blood cultures (pBC) may limit exposure to unnecessary or inappropriate antibiotics.

METHODS

Inpatients with pBC showing GPCC between October 2013 and December 2017 were included. In the baseline period (BL), final ID and susceptibility results were reported in the electronic medical record (EMR) within 48 h of telephoned Gram stain report. The laboratory introduced rapid phenotypic identification and direct susceptibility testing (INT1), later replaced by PCR (INT2). In the last Intervention (INT3), Antimicrobial Stewardship Response Team (ASRT) contacted providers with PCR results and recommendations.

RESULTS

Time to directed therapy (TDT) for MSSA and coagulase-negative Staphylococci (CoNS) decreased from BL to INT3 (48.5-17.9 h, 50.3-16.4 h, respectively). Time to ID from BL to INT3 for MSSA and CoNS also decreased (23.2-1.9 h, 44.7-2.8, respectively).

CONCLUSIONS

TDT can be improved by modification of reporting methods with utilization of an ASRT.

Optimization of antimicrobial therapy in vancomycin-resistant enterococcal bacteraemia using a rapid detection Gram-positive blood culture assay

Rapid molecular blood culture Gram-positive (BC-GP) assay can promptly identify vancomycin-resistant enterococcal (VRE) bloodstream infections (BSIs). We sought to evaluate patients with VRE BSI following the pre (N = 44) and post (N = 20) implementation of Verigene BC-GP assay. The average time to detection of VRE was 25.9 ± 4.1h (95% confidence interval (CI): 17.6-34.1; P < 0.001) earlier with Verigene BC-GP assay. Compared to patients in the pre-Verigene BC-GP period, the mean adjusted difference in time to administration of anti-VRE therapy was 18.2 ± 7.8h (95% CI: 2.5-33.8; P = 0.024) earlier among patients in the post-Verigene BC-GP period.

Incidence, prevalence, and management of MRSA bacteremia across patient populations-a review of recent developments in MRSA management and treatment

Methicillin-resistant Staphylococcus aureus (MRSA) infection is still a major global healthcare problem. Of concern is S. aureus bacteremia, which exhibits high rates of morbidity and mortality and can cause metastatic or complicated infections such as infective endocarditis or sepsis. MRSA is responsible for most global S. aureus bacteremia cases, and compared with methicillin-sensitive S. aureus, MRSA infection is associated with poorer clinical outcomes. S. aureus virulence is affected by the unique combination of toxin and immune-modulatory gene products, which may differ by geographic location and healthcare- or community-associated acquisition. Management of S. aureus bacteremia involves timely identification of the infecting strain and source of infection, proper choice of antibiotic treatment, and robust prevention strategies. Resistance and nonsusceptibility to first-line antimicrobials combined with a lack of equally effective alternatives complicates MRSA bacteremia treatment. This review describes trends in epidemiology and factors that influence the incidence of MRSA bacteremia. Current and developing diagnostic tools, treatments, and prevention strategies are also discussed.

Efficacy of Ceftaroline against Methicillin-Susceptible Staphylococcus aureus Exhibiting the Cefazolin High-Inoculum Effect in a Rat Model of Endocarditis

Certain Staphylococcus aureus strains exhibit an inoculum effect (InE) with cefazolin (CFZ) that has been associated with therapeutic failures in high-inoculum infections. We assessed the in vitro activities of ceftaroline (CPT), CFZ, and nafcillin (NAF) against 17 type A β-lactamase (βla)-producing, methicillin-susceptible S. aureus (MSSA) strains, including the previously reported TX0117, which exhibits the CFZ InE, and its βla-cured derivative, TX0117c. Additionally, we determined the pharmacokinetics of CPT in rats after single intramuscular doses of 20 and 40 mg/kg of body weight and evaluated the activities of CPT (40 mg/kg every 8 h [q8h]), CFZ, and NAF against TX0117 and TX0117c in a rat model of infective endocarditis. No InE was observed for CPT or NAF, whereas a marked InE was detected for CFZ (MIC, 8 to ≥128 μg/ml). CPT and NAF treatment against TX0117 resulted in mean bacterial counts of 2.3 and 2.1 log10 CFU/g in vegetations, respectively, compared to a mean of 5.9 log10 CFU/g in the CFZ-treated group (CPT and NAF versus CFZ, P = 0.001; CPT versus NAF, P = 0.9830). Both CFZ and CPT were efficacious against the βla-cured derivative, TX0117c, compared to time zero (t0) (P = <0.0001 and 0.0015, respectively). Our data reiterate the in vivo consequences of the CFZ InE and show that CPT is not affected by this phenomenon. CPT might be considered for high-inoculum infections caused by MSSA exhibiting the CFZ InE.

Improving time to optimal Staphylococcus aureus treatment using a penicillin-binding protein 2a assay

The penicillin-binding protein 2a (PBP2a) assay is a quick, accurate and inexpensive test for determining methicillin susceptibility in Staphylococcus aureus. A pre-post-study design was conducted using a PBP2a assay with and without the impact of an antimicrobial stewardship intervention to improve time to optimal therapy for methicillin-susceptible and methicillin-resistant S. aureus isolates. Our results demonstrate significantly improved time to optimal therapy and support the use of a PBP2a assay as part of an programme for all healthcare facilities, especially those with limited resources.

Rapid molecular determination of methicillin resistance in staphylococcal bacteraemia improves early targeted antibiotic prescribing: a randomized clinical trial

Empiric therapy of methicillin-susceptible Staphylococcus aureus (MSSA) infections with vancomycin is associated with poorer outcome than targeted therapy with β-lactams. Our objective was to evaluate whether rapid determination of methicillin resistance shortens the time from Gram stain to targeted antimicrobial therapy in staphylococcal bacteraemia, thereby reducing vancomycin overuse. This was a single-centre open parallel RCT. Gram-positive cocci in clusters in positive blood culture underwent real-time PCR for rapid species and methicillin resistance determination parallel to conventional microbiology. Patients were randomized 1:1 so that clinicians would be informed of PCR results (intervention group) or not (control group). Eighty-nine patients (intervention 48, control 41) were analysed. MRSA was identified in seven patients, MSSA in 46, and CoNS in 36. PCR results were highly concordant (87/89) with standard microbiology. Median time (hours) from Gram stain to transmission of methicillin-susceptibility was 3.9 (2.8-4.3) vs. 25.4 (24.4-26-7) in intervention vs. control groups (p <0.001). Median time (hours) from Gram stain to targeted treatment was similar for 'all staphylococci' [6 (3.8-10) vs. 8 (1-36) p 0.13] but shorter in the intervention group when considering S. aureus only [5 (3-7) vs. 25.5 (3.8-54) p <0.001]. When standard susceptibility testing was complete, 41/48 (85.4%) patients in the intervention group were already receiving targeted therapy compared with 23/41 (56.1%) in the control group (p 0.004). There was no significant effect on clinical outcomes. Rapid determination of methicillin resistance in staphylococcal bacteraemia is accurate and reduces significantly the time to targeted antibiotic therapy in the subgroup of S. aureus, thereby avoiding unnecessary exposure to vancomycin.

Impact of the multiplex polymerase chain reaction in culture-positive samples on appropriate antibiotic use in patients with staphylococcal bacteremia

Rapid identification of the microorganisms in patients with bacteremia may be useful in clinical practice. We evaluated the impact of the multiplex polymerase chain reaction (PCR) on appropriate antibiotic use for patients with gram-positive cocci cluster (GPCC) bacteremia. We divided the GPCC bacteremia cases into a pre-PCR group (2010-2011) and a post-PCR group (2012-2013). A total 664 cases were included in the pre-PCR group; and 570, in the post-PCR group. In methicillin-susceptible Staphylococcus aureus (MSSA) cases, optimal antibiotics were administered earlier in the post-PCR group (77.4h versus 42.6h, P=0.035). Although the proportions of glycopeptide exposure did not differ (54.7% versus 56.7%, P=0.799), the duration of exposure decreased (69.6h versus 30.7h, P=0.004). In methicillin-resistant S. aureus cases, the time to optimal antibiotics administration did not differ (45.4h versus 43.7h, P=0.275). Multiplex PCR test significantly improved the early initiation of optimal antibiotics in MSSA bacteremia and reduced the unnecessary glycopeptide exposure.

Antibiotic treatment algorithm development based on a microarray nucleic acid assay for rapid bacterial identification and resistance determination from positive blood cultures

Rapid diagnosis of bloodstream infections remains a challenge for the early targeting of an antibiotic therapy in sepsis patients. In recent studies, the reliability of the Nanosphere Verigene Gram-positive and Gram-negative blood culture (BC-GP and BC-GN) assays for the rapid identification of bacteria and resistance genes directly from positive BCs has been demonstrated. In this work, we have developed a model to define treatment recommendations by combining Verigene test results with knowledge on local antibiotic resistance patterns of bacterial pathogens. The data of 275 positive BCs were analyzed. Two hundred sixty-three isolates (95.6%) were included in the Verigene assay panels, and 257 isolates (93.5%) were correctly identified. The agreement of the detection of resistance genes with subsequent phenotypic susceptibility testing was 100%. The hospital antibiogram was used to develop a treatment algorithm on the basis of Verigene results that may contribute to a faster patient management.

Rapid molecular diagnostic tests in patients with bacteremia: evaluation of their impact on decision making and clinical outcomes

We performed a systematic review of the data regarding rapid diagnostic tests and their advantages or limitations on patients' clinical outcomes. The PubMed and Scopus databases were searched independently by two reviewers. Mortality was the primary outcome. Most studies compared rapid tests with blood cultures. Although not observed in all studies, only studies comparing rapid tests in conjunction with antimicrobial stewardship programs (ASPs) showed a mortality benefit. A reduction in hospital or intensive care unit (ICU) length of stay was also observed in almost all studies when the rapid tests, with or without ASPs, were used. Finally, treatment decisions were taken earlier in the rapid test groups. Despite a faster treatment decision, a clear mortality benefit was not seen when rapid tests were used. It is crucial to differentiate the influence of rapid tests from that of ASPs and clarify the actual effect of each factor separately.