Serology
IgG and IgM antibodies against the SARS-CoV-2 spike receptor binding domain (RBD) were measured using the AdviseDx SARS-CoV-2 IgM and IgG II (Abbott) chemiluminescent microparticle immunoassays (CMIA) on the Alinity platform. Threshold for positive on the qualitative IgM assay: Index ≥ 1.0 AU is positive, <1.0 AU is negative (from kit instructions). Index is relative fluorescence of sample, divided by relative fluorescence of calibrator, or index (S/C). Threshold for positive on the quantitative IgG assay is ≥50 AU/mL.