Abstract
Objective: To explore the diagnostic value of serum severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid (N) protein assay in the early stages of SARS-COV-2 infection.Methods: Serum N protein level in SARS-COV-2 infected patients and non-SARS-COV-2 infected population was measured by enzyme-linked immunosorbent assay (ELISA) double antibody sandwich assay. Colloidal gold immunochromatography assay was used to detect serum N protein antibodies in the above populations.Results: Fifty cases of SARS-CoV-2 nucleic acid-positive and SARS-CoV-2 antibody-negative patients had a serum N protein positivity rate of 76%. Thirty-seven patients who were positive for serum SARS-CoV-2 antibody after infection had a serum SARS-CoV-2 N protein positivity rate of 2.7%. Serum N protein test results of 633 non-SARS-COV-2 infected patients, including pregnant women, patients with other respiratory infections, and individuals with increased rheumatoid factor were all negative, with serum N protein concentration <10.00 pg/mL at 100% specificity. Using SPSS 19.0 to calculate the receiver operating characteristic curve, the area under the curve was determined to be 0.9756 (95% confidence interval 0.9485–1.000, p < 0.0001), and sensitivity and specificity were 92% (95% confidence interval 81.16–96.85%) and 96.84% (95% confidence interval 95.17–97.15%), respectively. The best CUT-OFF value was 1.850 pg/mL.Conclusion: The measurement of serum SARS-COV-2 N protein has a high diagnostic value for infected patients before the antibody appears and shortens the window period of serological diagnosis. It is recommended that the manufacturer establish two different CUT-OFF values according to the purpose of the application. One CUT-OFF value is used for the diagnosis of clinical SARS-COV-2 infection, and the other is used to screen out as many suspected cases as possible.
Highlights
As of July 10, 2020, there were more than 12.2 million people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and more than 554,291 deaths (Johns Hopkins University CSSE, 2020; https:// gisanddata.Maps.Arcgis.Com/apps/opsdashboard/index.Html#/ bda7594740fd40299423467b48e9ecf6), which has posed a serious threat to the health and economic life of people globally
All COVID-19 patients were diagnosed based on the results of nucleic acid Reverse Transcription-Polymerase Chain Reaction (RT-PCR) test, as well as pathological changes observed in computed tomography (CT) images, according to the seventh edition of the pneumonia diagnosis and treatment program for the novel Coronavirus infection reported by the (National Health Commission of the People’s Republic of China, 2020; http://www.nhc.gov.cn/y zygj/s7653p/202003/46c9294a7dfe4cef80dc7f5912eb1989.shtml)
The mean value, standard deviation (SD), and coefficient of variation (CV) of the results were calculated for 20 times
Summary
As of July 10, 2020, there were more than 12.2 million people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and more than 554,291 deaths (Johns Hopkins University CSSE, 2020; https:// gisanddata.Maps.Arcgis.Com/apps/opsdashboard/index.Html#/ bda7594740fd40299423467b48e9ecf6), which has posed a serious threat to the health and economic life of people globally. The diagnosis of SARS-COV-2 infection is mainly based on pharyngeal swab or sputum nucleic acid detection, and specific serum antibody detection is used as an auxiliary marker (To et al, 2020; http://www.nhc.gov.cn/yzygj/s7653p/202003/ 46c9294a7dfe4cef80dc7f5912eb1989.shtml). It is difficult to detect the infection at an early stage, making it difficult to block the source of infection, and this increases the difficulty of preventing and controlling the spread of SARS-COV-2 infection. Given this situation, this study analyzed the positivity rate of serum N protein before the generation of serum antibodies in patients infected with SARS-COV-2, providing new diagnostic indicators for the early detection of SARS-COV-2 infection
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