SARS-CoV-2 infection serology validation of different methods: Usefulness of IgA in the early phase of infection

ABSTRACT

In the late December 2019, an outbreak of pneumonia of unknown origin was reported in Wuhan, Hubei province, China. A novel coronavirus was isolated from the respiratory samples of patients with pneumonia as showed by the sequence analysis of the virus genomes obtained;The novel coronavirus was named SARSCoV-2. Reverse-transcriptase real-time PCR (rRT-PCR) is the method of choice for detecting SARS-CoV-2 infection. Despite the high sensitive of the real-time PCR tests, sometimes samples from the upper respiratory tract may result negative even in the presence of radiological findings of pneumonia probably due to the viral load in the upper respiratory tract is low compared to the lower respiratory tract;low quality of the collected sample or technical reasons linked to the assay used. The use of serological assays may help in making diagnosis. The antibody response to SARS-CoV-2 is not well understood yet, but the availability of sensitive and specific serological assays will be crucial for the early diagnosis of infection, for epidemiological studies, for defining the presence of neutralizing antibodies in response to a possible vaccine. In this work, we tested and compared the performances of one chemiluminescent immunoassay, two ELISA assays and an ECLIA assay. Among the platforms assessed in this study, the ECLIA serological assay performed best, and may be a valid screening method for SARS-COV-2 infection. The IgA detected by the ELISA assay might be a more reliable and stable early serological marker than IgM. Instead, IgGs, as expected, showed stable level after 10 days from symptoms onset. Taken together, if a reflex test could be set in the laboratory, the ECLIA method could be used as screening test, considering both the excellent performance and the cost per single test;while ELISA assay for IgG and IgA, which are present at a higher level than IgM and last longer, might be used as confirmatory test.