SARS-CoV-2 IgG/IgM Rapid Test as a Diagnostic Tool in Hospitalized Patients and Healthcare Workers, at a large Teaching Hospital in northern Italy, during the 2020 COVID-19 Pandemic

Abstract

We describe the outcome of a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) IgG/IgM rapid test, and discuss the potential suitability of antibody testing. Retrospective single cohort study on patients with suspected Coronavirus Disease 2019 (COVID-19) and asymptomatic Healthcare Workers, enrolled from March to April 2020. Subjects had quantitative PCR (qPCR) test for detection of SARS-CoV-2 via nasal swab and serological testing using the COVID-19 IgG/ IgM Rapid Test (PRIMA Lab SA) immunochromatographic assay. Some subjects underwent chemiluminescence immunoassay (CLIA) after rapid test. The aim of the study was to analyse the proportion of those who developed a positive IgM/IgG response for SARS-CoV-2. The correspondence between the results from rapid testing and CLIA, when available, was evaluated. 97 subjects underwent qPCR for SARS-CoV-2 through nasal swab, which resulted positive in 40/43 (93.0%) of symptomatic patients, 2/40 (5%) of asymptomatic HCW, in no subjects with suspected COVID- 19 (clinical and radiological findings) then excluded by repeated nasal swabs and alternative diagnosis (COVID-19-negative patients, CNPs), and in 6/6 (100%) of patients with confirmed diagnosis and negative follow-up nasal swabs (COVID-19-recovered patients, CRPs). IgM resulted positive in 8/43 (18.6%) of symptomatic patients and in 1/6 (16.7%) of CRPs. IgG resulted positive in 36/43 (83.7%) of symptomatic patients, 2/40 (5%) of HCW, and in 1/8 (12.5%) and 6/6 (100%) of CNPs and CRPs, respectively. A comparison between an IgG/IgM Rapid Test and a following CLIA test showed consistency in negative results in 25/28 of HCW and 8/8 of CNPs tested. Our preliminary data support the role of IgG/IgM Rapid Test (PRIMA Lab SA) immunochromatographic assay as a point-of-care test that may complement molecular tests in the screening of SARS-CoV-2 carriers. The test may gain particular relevance in shortening the time needed to refer patients to a COVID or non-COVID Hospital area and to achieve diagnosis in patients with persistently negative nasal swabs.

Keywords: COVID-19; IgG/IgM; SARS-CoV-2; antibody; rapid test; serological test.