ABSTRACT
Post-market surveillance of test performance is a critical function of public health agencies and clinical researchers that ensures diagnostics maintain performance characteristics following their regulatory approval. Changes in product quality, manufacturing processes over time, or the evolution of new variants may impact product quality. During the COVID-19 pandemic, a plethora of point-of-care tests (POCTs) were released onto the Canadian market. This study evaluated the performance characteristics of several of the most widely-distributed POCTs in Canada, including four rapid antigen tests (Abbott Panbio, BTNX Rapid Response, SD Biosensor, Quidel QuickVue) and two molecular tests (Abbott ID NOW, Lucira Check IT). All tests were challenged with 149 SARS-CoV-2 clinical positives, including multiple variants up to and including Omicron XBB.1.5, as well as 29 clinical negatives. Results were stratified based on whether the isolate was Omicron or pre-Omicron as well as by RT-qPCR Ct value. The test performance of each POCT was consistent with the manufacturers claims and showed no significant decline in clinical performance against any of the variants tested. These findings provide continued confidence in the results of these POCTs as they continue to be used to support decentralized COVID-19 testing. This work demonstrates the essential role of post-market surveillance in ensuring reliability in diagnostic tools.
Subject(s)
COVID-19ABSTRACT
The Cepheid(R) GeneXpert(R) Xpert(R) 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 the exception of an additional SARS-CoV-2 target that was included to improve assay robustness against emerging variants. The performance characteristics of the SARS-CoV-2/Flu/RSV PLUS combination test were assessed at the Lakeridge Health Oshawa Hospital Centre and the National Microbiology Laboratory of Canada. The PLUS Assay was directly compared to the Xpert Xpress SARS-CoV-2/Flu/RSV combination test using SARS-CoV-2 culture from five variants and remnant clinical specimens collected across multiple waves of the COVID-19 pandemic. This included 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. Additionally, 50 samples negative for all pathogens were included in this comparison. The PLUS Assay showed a high percent agreement with the widely used SARS-CoV-2/Flu/RSV combination test. Based on the findings from this study, the PLUS Assay and the Xpert SARS-CoV-2/Flu/RSV combination test results are largely consistent as there was no observed difference in sensitivity, specificity, reported Ct value, or time to result when challenged with various SARS-CoV-2 variants.
Subject(s)
COVID-19ABSTRACT
Throughout the COVID-19 pandemic, wastewater surveillance has been used to monitor trends in 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 the GeneXpert is a viable option for surveillance of SARS-CoV-2 in wastewater in locations that do not have access to established testing laboratories.
Subject(s)
COVID-19ABSTRACT
Objectives: Antigen-based rapid diagnostics tests (Ag-RDTs) are useful tools for SARS-CoV-2 detection. However, misleading demonstrations of the Abbott Panbio COVID-19 Ag-RDT on social media claimed that SARS-CoV-2 antigen could be detected in municipal water and food products. To offer a scientific rebuttal to pandemic misinformation and disinformation, this study explored the impact of using the Panbio SARS-CoV-2 assay with conditions falling outside of manufacturer recommendations. Methods: Using Panbio, various water and food products, laboratory buffers, and SARS-CoV-2-negative clinical specimens were tested, with and without manufacturer buffer. Additional experiments were conducted to assess the role of each Panbio buffer component (tricine, NaCl, pH, and tween-20), as well as the impact of temperatures (4{degrees}C, 20{degrees}C , and 45{degrees}C) and humidity (90%) on assay performance. Results: Direct sample testing (without the kit buffer), resulted in false positive signals resembling those obtained with SARS-CoV-2-positive controls tested under proper conditions. The likely explanation of these artifacts is non-specific interactions between the SARS-CoV-2-specific conjugated and capture antibodies, as proteinase K treatment abrogated this phenomenon, and thermal shift assays showed pH-induced conformational changes under conditions promoting artifact formation. Omitting, altering, and reverse engineering the kit buffer all supported the importance of maintaining buffering capacity, ionic strength, and pH for accurate kit function. Interestingly, the Panbio assay could tolerate some extremes of temperature and humidity outside of manufacturer claims. Conclusions: Our data support strict adherence to manufacturer instructions to avoid false positive SARS-CoV-2 Ag-RDT reactions, otherwise resulting in anxiety, overuse of public health resources, and dissemination of misinformation.
Subject(s)
COVID-19 , Anxiety DisordersABSTRACT
The coronavirus disease 2019 (Covid-19) pandemic, caused by SARS-CoV-2, has resulted in a global testing supply shortage. In response, pooled testing has emerged as a promising strategy that can immediately increase testing capacity. Here, we provide support for the adoption of sample pooling with the point-of-care Cepheid Xpert(R) Xpress SARS-CoV-2 molecular assay. Corroborating previous findings, the Xpert(R) Xpress SARS-CoV-2 assay limit of detection was comparable to central laboratory reverse-transcription quantitative PCR tests with observed SARS-CoV-2 detection below 100 copies/mL. The Xpert(R) Xpress assay detected SARS-CoV-2 after samples with minimum viral loads of 461 copies/mL were diluted into six sample pools. Based on these data, we recommend the adoption of pooled testing with the Xpert(R) Xpress SARS-CoV-2 assay where warranted by population public health needs. The suggested number of samples per pool, or pooling depth, is unique for each point-of-care test site and should be determined by assessing positive test rates. To statistically determine appropriate pooling depth, we have calculated the pooling efficiency for numerous combinations of pool sizes and test rates. This information is included as a supplemental dataset that we encourage public health authorities to use as a guide to make recommendations that will maximize testing capacity and resource conservation.