Comparison of various serological assays for novel SARS-COV-2.

Coronavirus disease-19 (COVID19), the novel respiratory illness caused by severe acute respiratory syndrome coronavirus (SARS-CoV-2), is associated with severe morbidity and mortality. The aim of our study was to compare different immunoassays. We evaluated three immunochromatographic test (The StrongStep®SARS-CoV-2 IgG/IgM kit, AllTest COV-19 IgG/IgM kit, and Wondfo® SARS-CoV-2 Antibody) and two chemiluminescence immunoassays (CMIA) (Covid-19 VIRCLIA® IgM+IgA/IgG monotest and the Abbott SARS-CoV-2 IgG assay) in COVID-19 patients. The assays were performed using serum samples of three group patients, i.e., healthy controls, patients with SARS-CoV-2 PCR positive, and patients with SARS-CoV-2 PCR negative clinically diagnosed of COVID-19 infection. The detection percentages of IgG with the StrongStep® SARS-CoV-2 IgG/IgM kit and AllTest COV-19 IgG/IgM kit were similar in both groups (83.3% and 80.6%, respectively in group 2, p = 0.766) and (42.9% and 50.0%, respectively in group 3, p = 0.706). There were some differences on IgM detection between StrongStep® SARS-CoV-2 IgG/IgM kit and AllTest COV-19 IgG/IgM kit (11.1% and 30.6%, respectively in group 2, p = 0.042 and 0.0% and 28.6%, respectively in group 3, p = 0.031). The positive rate of IgG in group 2 is higher compared to group 3 with the two immunoassays tested. We observe the same positive rates of IgG with the two CMIA. Our study shows excellent performance of CMIA compared to immunochromatographic test and confirms its potential use in the diagnosis of the new SARS-CoV-2.

Amplification of human β-glucoronidase gene for appraising the accuracy of negative SARS-CoV-2 RT-PCR results in upper respiratory tract specimens

Real-time reverse transcription polymerase-chain reaction (RT-PCR) is the mainstay of Covid-19 diagnosis. False-negative RT-PCR results may hamper clinical management of patients and hinder the adoption of epidemiological measures to control the pandemic. The current study was aimed at assessing whether amplification of {beta}-glucoronidase (GUSB) gene would help estimate the accuracy of SARS-CoV-2 RT-PCR negative results in upper respiratory tract (URT) specimens. URT specimens that tested negative by SARS-CoV-2 RT-PCR displayed higher GUSB RT-PCR cycle thresholds (CT) (P=0.070) than those testing positive (median, 30.7; range, 27.0-40.0, and median 29.7; range 25.5-36.8, respectively), this reflecting poorer cellularity. Receiver operating characteristic (roc) curve analysis indicated that a CT threshold of 31.2 discriminated best between positive and negative SARS CoV-2 RT-PCRs (area under a curve, 0.66; 95% CI, 0.50-0.81; P=0.08). This cut-off yielded a true negative ratio of 89% and accuracy of 70%. The data suggested that amplification of the GUSB gene by RT-PCR may help to appraise the accuracy of negative SARS-CoV-2 RT-PCR results in patients in whom Covid-19 is eventually diagnosed.