SARS-CoV-2 sample-to-answer nucleic acid testing in a tertiary care emergency department: evaluation and utility

Rapid sample-to-answer tests for detection of SARS-CoV-2 are emerging and data on their relative performance is urgently needed. We evaluated the analytical performance of two rapid nucleic acid tests, Cepheid Xpert^® Xpress SARS-CoV-2 and Mobidiag Novodiag^® Covid-19, in comparison to a combination reference of three large-scale PCR tests. Moreover, utility of the Novodiag^® test in tertiary care emergency departments was assessed. In the preliminary evaluation, analysis of 90 respiratory samples resulted in 100% specificity and sensitivity for Xpert^®, whereas analysis of 107 samples resulted in 93.4% sensitivity and 100% specificity for Novodiag^®. Rapid SARS-CoV-2 testing with Novodiag^® was made available for four tertiary care emergency departments in Helsinki, Finland between 18 and 31 May, coinciding with a rapidly declining epidemic phase. Altogether 361 respiratory specimens, together with relevant clinical data, were analyzed with Novodiag^® and reference tests: 355/361 of the specimens were negative with both methods, and 1/361 was positive in Novodiag^® and negative by the reference method. Of the 5 remaining specimens, two were negative with Novodiag^®, but positive with the reference method with late Ct values. On average, a test result using Novodiag^® was available nearly 8 hours earlier than that obtained with the large-scale PCR tests. While the performance of novel sample-to-answer PCR tests need to be carefully evaluated, they may provide timely and reliable results in detection of SARS-CoV-2 and thus facilitate patient management including effective cohorting.