Clinical evaluation of the GeneXpert® Xpert® Xpress SARS-CoV-2/Flu/RSV combination test

Utility of the Xpert Xpress CoV-2/Flu/RSV Plus Kit: A Glance at RSV Infection in Adults and Coinfection Rate

Background

Viral infection is responsible for the majority of respiratory tract infections (RTI). This retrospective study evaluates the advantages of using the multiplex Xpert Xpress CoV-2/Flu/RSV plus kit in laboratory diagnosis of RTI caused by the most related viruses.

Materials and Methods

Data were obtained from medical records between November 2021 and May 2023 for any sample tested using either the Xpert Xpress Flu/RSV kit, Xpert Xpress Flu kit, Xpert Xpress SARS-CoV-2 kit, and Xpert Xpress CoV-2/Flu/RSV plus kit.

Results

Influenza virus A was detected in 8.5% (55/649) of the samples using the Flu PCR kit and in 4.9% (123/2538) using CoV-2/Flu/RSV plus kit, while influenza virus B detection rates were 3.7% (24/649) using the Flu PCR kit and 1.7% (43/2538) using the CoV-2/Flu/RSV plus kit. However, the detection rates using the two kits were comparable when evaluated for the same time period of the year. SARS-CoV-2 infections were detected in 16.9% (1545/9153) and 10.5% (266/2538) of the cases using the SARS-CoV-2 kit and CoV-2/Flu/RSV plus kits, respectively. Respiratory syncytial virus (RSV) was identified in 17.7% (66/372) of children using Flu/RSV kit; this number dropped significantly when age-targeted testing of RSV was performed due to involvements of adults. With the CoV-2/Flu/RSV plus kit, about 34% (35/103) of RSV infections detected were in patients aged >20 years; these cases would have previously been overlooked because adults are not routinely tested for RSV using the Flu/RSV kit. All coinfection cases (n = 16) were only detected with the CoV-2/Flu/RSV plus kit.

Conclusion

The use of Xpert Xpress CoV-2/Flu/RSV plus kit not only results in shorter turnaround times through accurate detection of all four viruses, but also provides information on RSV infection in adults and coinfection rates.

Lessons from the pandemic: new best practices in selecting molecular diagnostics for point-of-care testing of infectious diseases in sub-Saharan Africa

INTRODUCTION

Point-of-care molecular diagnostics offer solutions to the limited diagnostic availability and accessibility in resource-limited settings. During the COVID-19 pandemic, molecular diagnostics became essential tools for accurate detection and monitoring of SARS-CoV-2. The unprecedented demand for molecular diagnostics presented challenges and catalyzed innovations which may provide lessons for the future selection of point-of-care molecular diagnostics.

AREAS COVERED

We searched PubMed from January 2020 to August 2023 to identify lessons learned from the COVID-19 pandemic which may impact the selection of point-of-care molecular diagnostics for future use in sub-Saharan Africa. We evaluated this in the context of REASSURED criteria (Real-time connectivity; Ease of specimen collection; Affordable; Sensitive; Specific; User-friendly; Rapid and robust; Equipment free; and Deliverable to users at the point of need) for point-of-care diagnostics for resource-limited settings.

EXPERT OPINION

The diagnostic challenges and successes during the COVID-19 pandemic affirmed the importance of the REASSURED criteria but demonstrated that these are not sufficient to ensure new diagnostics will be appropriate for public health emergencies. Capacity for rapid scale-up of diagnostic testing and transferability of assays, data, and technology are also important, resulting in updated REST-ASSURED criteria. Few diagnostics will meet all criteria, and trade-offs between criteria will need to be context-specific.

Clinical evaluation of the GeneXpert® Xpert® Xpress SARS-CoV-2/Flu/RSV PLUS combination test

The GeneXpert^® Xpert^® Xpress SARS-CoV-2/Flu/RSV PLUS combination test (PLUS assay) received Health Canada approval in January 2022. The PLUS assay is similar to the SARS-CoV-2/Flu/RSV combination test, with modifications to improve assay robustness against circulating and emerging variants. The performance characteristics of the PLUS assay were assessed at the Lakeridge Health Oshawa Hospital Centre and the National Microbiology Laboratory of Canada. The PLUS assay was directly compared to the SARS-CoV-2/Flu/RSV combination test using SARS-CoV-2 culture from five variants and remnant clinical specimens collected across the coronavirus disease 2019 pandemic. This included 50 clinical specimens negative for all pathogens, 110 clinical specimens positive for SARS-CoV-2, influenza A, influenza B, RSVA, and(or) RSVB and an additional 11 mixed samples to screen for target interactions. The PLUS assay showed a high % agreement with the widely used SARS-CoV-2/Flu/RSV combination test. Based on these findings, the PLUS assay and the Xpert SARS-CoV-2/Flu/RSV combination test results are largely consistent with no observed difference in sensitivity, specificity, or time to result when challenged with various SARS-CoV-2 variants. The reported cycle threshold (Ct) values provided by the new PLUS assay were also unchanged, with the exception of a possible 1-2 decrease reported in Ct for RSVA across a limited sample size.

Single-Center Experience in Detecting Influenza Virus, RSV and SARS-CoV-2 at the Emergency Department

Reverse transcription polymerase chain reaction (RT-PCR) on respiratory tract swabs has become the gold standard for sensitive and specific detection of influenza virus, respiratory syncytial virus (RSV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this retrospective analysis, we report on the successive implementation and routine use of multiplex RT-PCR testing for patients admitted to the Internal Medicine Emergency Department (ED) at a tertiary care center in Western Austria, one of the hotspots in the early coronavirus disease 2019 (COVID-19) pandemic in Europe. Our description focuses on the use of the Cepheid^® Xpert^® Xpress closed RT-PCR system in point-of-care testing (POCT). Our indications for RT-PCR testing changed during the observation period: From the cold season 2016/2017 until the cold season 2019/2020, we used RT-PCR to diagnose influenza or RSV infection in patients with fever and/or respiratory symptoms. Starting in March 2020, we used the RT-PCR for SARS-CoV-2 and a multiplex version for the combined detection of all these three respiratory viruses to also screen subjects who did not present with symptoms of infection but needed in-hospital medical treatment for other reasons. Expectedly, the switch to a more liberal RT-PCR test strategy resulted in a substantial increase in the number of tests. Nevertheless, we observed an immediate decline in influenza virus and RSV detections in early 2020 that coincided with public SARS-CoV-2 containment measures. In contrast, the extensive use of the combined RT-PCR test enabled us to monitor the re-emergence of influenza and RSV detections, including asymptomatic cases, at the end of 2022 when COVID-19 containment measures were no longer in place. Our analysis of PCR results for respiratory viruses from a real-life setting at an ED provides valuable information on the epidemiology of those infections over several years, their contribution to morbidity and need for hospital admission, the risk for nosocomial introduction of such infection into hospitals from asymptomatic carriers, and guidance as to how general precautions and prophylactic strategies affect the dynamics of those infections.

Clinical Evaluation of BioFire COVID-19 Test, BioFire Respiratory Panel 2.1, and Cepheid Xpert Xpress SARS-CoV-2 Assays for Sample-to-Answer Detection of SARS-CoV-2

Background: Due to the extreme infectivity of SARS-CoV-2, sample-to-answer SARS-CoV-2 reverse transcription (RT) polymerase chain reaction (PCR) assays are urgently needed in order to facilitate infectious disease surveillance and control. The purpose of this study was to evaluate three sample-to-answer SARS-CoV-2 RT-PCR assays—BioFire COVID-19 Test, BioFire RP 2.1, and Cepheid Xpert Xpress SARS-CoV-2—using clinical samples. Methods: A total of 77 leftover nasopharyngeal swab (NP) swabs (36 positives and 41 negatives) confirmed by reference SARS-CoV-2 RT real-time (q) PCR assay were collected. The clinical sample concordance, as specified by their respective emergency use authorizations (EUAs), in comparison to the reference SARS-CoV-2 RT-qPCR assay, was assessed. Results: The results showed that all three sample-to-answer SARS-CoV-2 RT-PCR assays provided perfectly concordant results consistent with the reference SARS-CoV-2 RT-qPCR assay. The BioFire COVID-19 Test exhibited the best turnaround time (TAT) compared to the other assays, regardless of the test results, using one-way analysis of variance followed by Scheffe’s post hoc test (p < 0.001). The Xpert Xpress SARS-CoV-2 showed a shorter average TAT (mean ± standard deviation, 49.9 ± 3.1 min) in the positive samples compared to that (55.7 ± 2.5 min) of the negative samples. Conclusions: Our evaluation demonstrates that the BioFire COVID-19 Test, BioFire RP 2.1, and Cepheid Xpert Xpress SARS-CoV-2 assays compare favorably to the reference SARS-CoV-2 RT-qPCR assay, along with a 100% concordance in assay results for clinical samples and an acceptable analytical performance at their guaranteed limits of detection. The addition of a widely used simultaneous sample-to-answer SARS-CoV-2 RT-PCR assay will contribute to the number of medical laboratories able to test for COVID-19.

Rapid Evaluation of the Xpert® Xpress CoV-2 plus and Xpert® Xpress CoV-2/Flu/RSV plus Tests

The Xpert^® Xpress SARS-CoV-2 and Xpert^® Xpress SARS-CoV-2/Flu/RSV tests were rapidly developed and widely used during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. In response to emerging genetic variability, a new SARS-CoV-2 target (RNA-dependent RNA-polymerase) has been added to both tests: Xpert^® Xpress CoV-2 plus and Xpert^® Xpress CoV-2/Flu/RSV plus test. A rapid evaluation of both tests was performed in South Africa, using residual respiratory specimens. Residual respiratory specimens (n = 125) were used to evaluate the Xpert^® Xpress CoV-2 plus test and included 50 genotyped specimens. The Xpert^® Xpress CoV-2/Flu/RSV plus test was assessed using 45 genotyped SARS-CoV-2 specimens, 10 influenza A, 10 influenza B and 20 respiratory syncytial virus specimens. Results were compared to in-country standard-of-care tests. Genotyped specimens tested the performance of the test under pressure from circulating SARS-CoV-2 variants of concern. Reference material was included to assess the test limits and linearity. The Xpert^® Xpress CoV-2 plus test performance compared to reference results across residual respiratory specimens was good (positive percentage agreement (PPA) = 95.2%, negative percentage agreement (NPA) = 95.0%) The Xpert^® Xpress CoV-2/Flu/RSV plus test showed good performance across all residual respiratory specimens (PPA = 100%, NPA = 98.3%). All genotyped variants of concern were detected by both tests. The Xpert^® Xpress CoV-2 plus and Xpert^® Xpress CoV-2/Flu/RSV plus tests can be used to diagnose SARS-CoV-2, and to diagnose and differentiate SARS-CoV-2, influenza A, influenza B and respiratory syncytial virus, respectively. The NPA was lower than the recommended 99%, but was influenced by the low number of negative specimens tested. The variants of concern assessed did not affect test performance. It is recommended that sites perform their own assessments compared to in-country standard-of-care tests.

Principles and Applications of Loop-Mediated Isothermal Amplification to Point-of-Care Tests

For the identification of nucleic acids, which are important biomarkers of pathogen-mediated diseases and viruses, the gold standard for NA-based diagnostic applications is polymerase chain reaction (PCR). However, the requirements of PCR limit its application as a rapid point-of-care diagnostic technique. To address the challenges associated with regular PCR, many isothermal amplification methods have been developed to accurately detect NAs. Isothermal amplification methods enable NA amplification without changes in temperature with simple devices, as well as faster amplification times compared with regular PCR. Of the isothermal amplifications, loop-mediated isothermal amplification (LAMP) is the most studied because it amplifies NAs rapidly and specifically. This review describes the principles of LAMP, the methods used to monitor the process of LAMP, and examples of biosensors that detect the amplicons of LAMP. In addition, current trends in the application of LAMP to smartphones and self-diagnosis systems for point-of-care tests are also discussed.

Comparative Performance Evaluation of FilmArray BioFire RP2.1 and MAScIR 2.0 Assays for SARS-CoV-2 Detection

Background

RT-PCR is the gold standard for COVID-19 diagnosis, but the lack of standardization of assays, whose diagnostic performance may widely vary, complicates the interpretation of the discrepancies that may be encountered. Study design. We conducted a retrospective study over a ten-month period at the Central Laboratory of Virology of Ibn Sina University Hospital of Rabat. We included nasopharyngeal swabs, positive and negative for SARS-CoV-2 on FilmArray BioFire® Respiratory Panel 2.1 Plus, which were subjected to our laboratory's reference test, MAScIR SARS-CoV-2 M kit 2.0, initially or after a freeze-thaw cycle. The results were compared, and each discrepant sample with sufficient volume underwent the third test, using ARGENE® SARS-CoV-2 R-GENE kit.

Results

Of 80 SARS-CoV-2 negative samples on FilmArray, there were no discordant results, whereas of 80 SARS-CoV-2 positive samples on FilmArray, 21 had discordant results on MAScIR, and only 11 could be tested on ARGENE, revealing positive results in 6 cases. 12.7% and 76.5% correspond to the discordance rates for MAScIR (with one or both targets detected on FilmArray), while 14.3% and 100% correspond to those of ARGENE. As the estimated sensitivity and specificity of FilmArray, compared with MAScIR, were 100% and 79.2%, respectively, its lower limit of detection, and ARGENE assay results, made it difficult to distinguish between false positives on FilmArray and false negatives on MAScIR without further investigations.

Conclusion

The implementation of a new assay in our laboratory revealed discrepancies suggesting a lack of sensitivity of our laboratory's reference test, leading us consequently to retain the SARS-CoV-2 positive result of these discordant samples on FilmArray, regardless of the detection of one or both targets. Our study, which is, to our knowledge, the first comparing FilmArray RP2.1 and MAScIR 2.0 assays for SARS-CoV-2 detection, highlights the urgent need to standardize RT-PCR assays for COVID-19 diagnosis.

A Sensitive and Rapid Wastewater Test for SARS-COV-2 and Its Use for the Early Detection of a Cluster of Cases in a Remote Community

Throughout the coronavirus disease 2019 (COVID-19) pandemic, wastewater surveillance has been used to monitor trends in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) prevalence in the community. A major challenge in establishing wastewater surveillance programs, especially in remote areas, is the need for a well-equipped laboratory for sample analysis. Currently, no options exist for rapid, sensitive, mobile, and easy-to-use wastewater tests for SARS-CoV-2. The performance of the GeneXpert system, which offers cartridge-based, rapid molecular clinical testing for SARS-CoV-2 in a portable platform, was evaluated using wastewater as the input. The GeneXpert demonstrated a SARS-CoV-2 limit of detection in wastewater below 32 copies/mL with a sample processing time of less than an hour. Using wastewater samples collected from multiple sites across Canada during February and March 2021, a high overall agreement (97.8%) was observed between the GeneXpert assay and laboratory-developed tests regarding the presence or absence of SARS-CoV-2. Additionally, with the use of centrifugal filters, the detection threshold of the GeneXpert system was improved to <10 copies/mL in wastewater. Finally, to support on-site wastewater surveillance, GeneXpert testing was implemented in Yellowknife, a remote community in Northern Canada, where its use successfully alerted public health authorities to undetected transmission of COVID-19. The identification of SARS-CoV-2 in wastewater triggered clinical testing of recent travelers and identification of new COVID-19 cases/clusters. Taken together, these results suggest that GeneXpert is a viable option for surveillance of SARS-CoV-2 in wastewater in locations that do not have access to established testing laboratories.

IMPORTANCE Wastewater-based surveillance is a powerful tool that provides an unbiased measure of COVID-19 prevalence in a community. This work describes a sensitive wastewater rapid test for SARS-CoV-2 based on a widely distributed technology, the GeneXpert. The advantages of an easy-to-use wastewater test for SARS-CoV-2 are clear: it supports surveillance in remote communities, improves access to testing, and provides faster results allowing for an immediate public health response. The application of wastewater rapid testing in a remote community facilitated the detection of a COVID-19 cluster and triggered public health action, clearly demonstrating the utility of this technology. Wastewater surveillance will become increasingly important in the postvaccination pandemic landscape as individuals with asymptomatic/mild infections continue transmitting SARS-CoV-2 but are unlikely to be tested.