Performance of the RT-LAMP-based eazyplex® SARS-CoV-2 as a novel rapid diagnostic test.

BACKGROUND: Diagnostic assays for severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2) that are easy to perform and produce fast results are essential for timely decision making regarding the isolation of contagious individuals. OBJECTIVE: We evaluated the CE-approved eazyplex® SARS-CoV-2, a ready-to-use real time RT-LAMP assay for identification of the SARS-CoV-2 N and ORF8 genes from swabs in less than 30 min without RNA extraction. STUDY DESIGN: Oropharyngeal and nasal swabs from 100 positive and 50 negative patients were inoculated into 0.9 % saline and tested by NeuMoDx™ RT-PCR. An aliquot was diluted fivefold in Copan sputum liquefying (SL) solution and directly analyzed by eazyplex® SARS-CoV-2. In addition, 130 patient swabs were prospectively tested with both methods in parallel. Analytical sensitivity of the assay was determined using virus stock dilutions. RESULTS: Positive percent agreement (PPA) between the eazyplex® SARS-CoV-2 and RT-PCR was 74 % for samples with Ct values < 35. When using a Ct cut-off ≤ 28 the PPA increased to 97.4 %. In the prospective part of the study overall PPA of the eazyplex® kit was 66.7 % but increased to 100 % when only Ct values ≤ 28 were considered. There were no false positive results. The median time to positivity was 12.5 min for the N gene and 16.75 min for ORF8. Analytical sensitivity was 3.75 TCID50/mL. 105 virus copies/mL were reproducibly detected. CONCLUSION: The eazyplex® SARS-CoV-2 is a rapid assay that accurately identifies samples with high viral loads. It may be useful for near-patient testing outside of a molecular diagnostic laboratory.

Use of the variplex™ SARS-CoV-2 RT-LAMP as a rapid molecular assay to complement RT-PCR for COVID-19 diagnosis.

BACKGROUND: Molecular assays based on reverse transcription-loop-mediated isothermal amplification (RT-LAMP) may be useful for rapid diagnosis of the severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2) because of the easy performance and the option to bypass RNA extraction. OBJECTIVES: This study was designed to evaluate the clinical performance of the CE-labeled variplexTM real time SARS-CoV-2 RT-LAMP assay in comparison to commercial RT-PCRs. STUDY DESIGN: RNA extracted from pharyngeal swabs was tested by variplex™ RT-LAMP and Corman's LightMix™ E gene RT-PCR as reference. Samples of respiratory secretions from Coronavirus infection disease (COVID-19) and negative control patients were analyzed by variplex™ without RNA extraction and tested in parallel with the Allplex™ and VIASURE BD MAX RT-PCRs. RESULTS: Using isolated RNA variplex™ RT-LAMP showed a sensitivity of 75 % compared to LightMix E gene RT-PCR but contrary to the latter it produced no false-positive results. For the evaluation of samples from respiratory secretions concordance analysis showed only a moderate agreement between the variplex™ RT-LAMP conducted on unprocessed samples and Allplex™ and VIASURE RT-PCRs (Cohen's κ ranging from 0.52-0.56). Using the approach to define a sample as true-positive when at least two assays gave a positive result the clinical sensitivities were as follows: 76.3 % for variplex™, 84.2 % for Allplex™ and 68.4 % for VIASURE. However, when results of RT-PCR and RT-LAMP were combined diagnostic sensitivity was increased to 92-100 %. CONCLUSION: The variplex RT-LAMP may serve as a rapid test to be combined with a RT-PCR assay to increase the diagnostic accuracy in patients with suspected COVID-19 infection.