The number of anatomical sites with detectable viral loads by RT-qPCR appeared to correlate with death risk.

No abstract

Using paired serum samples obtained from patients with illness associated with increases in anti-human coronavirus OC43 (HCoV-OC43) or anti-HCoV-229E antibodies, we examined the possibility of false-positive results detected in a recombinant severe acute respiratory syndrome (SARS)-associated coronavirus (SARSCoV) nucleocapsid protein immunoglobulin G enzyme-linked immunosorbent assay (ELISA). Three of the 21 and 1 of the 7 convalescent-phase serum samples from persons with increases in antibodies against HCoV-OC43 and HCoV-229E, respectively, tested positive by the recombinant SARS-CoV nucleocapsid protein-based ELISA. None of these samples were found to contain a specific antibody in the recombinant SARS-CoV spike polypeptide-based Western blot assay.Severe acute respiratory syndrome (SARS), caused by SARS-associated coronavirus (SARS-CoV), has affected 30 countries in five continents, with more than 8,000 cases and 750 deaths (7-11). As for the detection of antibodies against SARS-CoV, at the moment, the most widely used methods are antibody detection in acute-and convalescent-phase sera by indirect immunofluorescence assay and enzyme-linked immunosorbent assay (ELISA) using cell culture extracts (4,8,10). However, antibody detection by these methods may be less reproducible, more difficult to standardize, and more laborintensive than ELISA-based antibody detection tests using recombinant antigens. Furthermore, producing the infected cell lines for coating the ELISA plates and the slides for indirect immunofluorescence requires cultivation of the SARS-CoV, for which biosafety level 3 laboratory facilities are required. Such facilities are not available in most clinical microbiology laboratories.ELISA-based antibody detection tests using recombinant antigens are well known to offer higher reproducibility and to be easier to standardize and less labor-intensive than antibody detection by indirect immunofluorescence assay and ELISA using cell culture extract, and they do not require cultivation of the SARS-CoV (1, 2, 14, 18). Recently, we have reported the use of recombinant SARS-CoV nucleocapsid protein ELISAbased antibody tests for serodiagnosis of SARS-CoV pneumonia and the study of the seroprevalence of nonpneumonic SARS-CoV infections (15, 16). In addition, others have also reported the use of recombinant-protein-based immunoassays for serodiagnosis of SARS-CoV pneumonia (3, 17). However, in our studies, we have also shown that false-positive reactions were detected if the recombinant SARS-CoV nucleocapsid protein-based ELISA was used alone for antibody detection (15). In this study, using paired serum samples obtained from patients with increases in anti-human CoV OC43 (HCoV-OC43) or anti-HCoV-229E antibodies, we examined the possibility of false-positive results detected by the recombinant SARS-CoV nucleocapsid protein-based ELISA. The importance of using Western blot assays, with the nucleocapsid protein and spike polypeptide of SARS-CoV, for confirmation was also determined.Paired serum samples collecte...