Evaluation of three commercial assays for SARS-CoV-2 molecular detection in upper respiratory tract samples

Liotti, Flora Marzia; Menchinelli, Giulia; Marchetti, Simona; Morandotti, Grazia Angela; Sanguinetti, Maurizio; Posteraro, Brunella; Cattani, Paola

The increasing COVID-19 widespread has created the necessity to assess the diagnostic accuracy of newly introduced (RT-PCR based) assays for SARS-CoV-2 RNA detection in respiratory tract samples. We compared the results of the Allplex™ 2019-nCoV assay with those of the Simplexa™ COVID-19 Direct assay and the Quanty COVID-19 assay, respectively, all performed on 125 nasal/oropharyngeal swab samples of patients with COVID-19 suspicion. Fifty-four samples were positive, and 71 were negative with the Allplex™ assay, whereas 47 of 54 samples were also positive with the Simplexa™ assay. The Quanty assay detected 55 positive samples, including the 54 positive samples with the Allplex™ assay and 1 sample that was Allplex™ negative but Simplexa™ positive. Using a consensus result criterion as the reference standard allowed to resolve the eight samples with discordant results (one Allplex™ negative and seven Simplexa™ negative) as truly false negative. Interestingly, a Spearman’s negative association was found between the viral RNA loads quantified by the Quanty assay and the C(T) values of RT PCRs performed with either the Allplex™ assay or the Simplexa™ assay. However, the strength of this association was higher for the Allplex™ assay (N gene, ρ = − 0.92; RdRP gene, ρ = − 0.91) than for the Simplexa™ assay (ORF1ab gene, ρ = − 0.65; S gene, ρ = − 0.80). The Allplex™ 2019-nCoV, the Simplexa™ COVID-19 Direct, and the Quanty COVID-19 assays yielded comparable results. However, the role these assays might play in future clinical practice warrants larger comparison studies. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10096-020-04025-0) contains supplementary material, which is available to authorized users.