[Antibody Response as Assessed by A Rapid Immunochromatographic Assay in Patients with COVID-19 Pneumonia Caused by the Novel Coronavirus, SARS-CoV-2]

ABSTRACT

An immunochromatographic assay that has been developed for the detection of antibodies in blood-derived specimens is raising expectations for the diagnosis of COVID-19, the disease caused by the novel corona virus SARS-CoV-2. Herein, we studied the interval from symptom onset to the first positive results of the immunochromatographic assay for IgM and IgG antibodies in 52 patients with a definitive diagnosis of COVID-19 (disease confirmed by the PCR test). Furthermore, we also examined the test results in 35 patients with acute fever and pneumonia who were negative by the PCR test. All patients with a definitive diagnosis of COVID-19 were confirmed to be antibody-positive. The mean time from symptom onset to the first positive result for IgM antibody was 11.9 days (minimum 5, median 11), and that to the first positive result for IgG antibody was 11.2 days (minimum 5, median 11). No significant difference was observed between the tests for IgM and IgG antibodies in terms of the percentage of positive patients or the interval from first onset to the first positive test result. There were no patients in whom the test for IgM became positive before the test for IgG. In 45 patients (87%), both IgM and IgG became positive at the same time, and in the remaining 7 patients (13%), the test for IgG became positive before that for IgM. Of 35 patients with acute fever and pneumonia who tested negative by the PCR test for SARS-CoV-2, not COVID-19, 6 (17.1%) and 1 (2.8%) showed positive results for anti-IgG antibody and anti-IgM antibody, respectively. Our study results were quite limited, and we do not intend to conduct a performance evaluation of the reagents contained in the detection kits. Assessment of antibody detection reagents for the immunochromatographic assay, which can be used as a complementary test to PCR, is expected in the future;however, the findings should be reviewed carefully.