Methods
The data described were obtained from two sources. The first is from our diagnostic operation for SARS-CoV-2 testing in a Clinical Laboratory Improvement Amendments (CLIA) Certified Respiratory Virus Diagnostic Laboratory (ID#: 45D0919666) that began on March 18, 2020.9 The second source came from rtPCR positive SARS-CoV-2 patients who enrolled in our ongoing study to evaluate antibody response kinetics after their primary infection. We included patients with 2 or more positive rtPCR tests for SARS-CoV-2 that were at least 70 days apart in order to fully capture a spectrum of patients with prolonged viral RNA shedding vs re-infection.
Based on proposed re-infection criteria in the literature, we defined three separate criteria to classify a patient as having a re-infection with SARS-CoV-2. These criteria are (1) a positive SARS-CoV-2 rtPCR test at least 90 days after individuals first became symptomatic with SARS-CoV-2 and subsequently become asymptomatic,4 (2) at least 2 negative rtPCR tests for SARS-CoV-2 between two positive tests,10,11 and (3) at least one negative rtPCR test for SARS-CoV-2 between two positive tests more than 28 days apart.12 For our analysis, only one criterion was needed to be considered a probable re-infection.
We collected demographic, laboratory, and clinical data from retrospective chart review as well as performed phone interviews using a structured questionnaire. The protocol was approved by the institutional review board at Baylor College of Medicine.
rtPCR Assays
Mid-turbinate swabs were tested for SARS-CoV-2 using CDC’s EUA for CDC 2019-Novel Coronavirus (2019-nCoV) rtPCR Diagnostic Panel. (Primers and probes target the nucleocapsid (N) gene (N1 and N2) of SARS-CoV-2 and ribonuclease P (RNase-P) gene). The samples were considered positive if N1, N2, and RNaseP cycle threshold (CT) values were <40.9
IgG Assay
The humoral IgG anti-spike enzyme linked immunosorbent assays (ELISA) were performed as part of our IRB approved research study. The SARS-CoV-2 full spike (S) protein used in the ELISA was kindly provided by Gale Smith (Novavax, Gaithersburg, MD).13 The samples were considered serologically positive if the Optical Density (OD) values were ≥0.5 at a serum dilution of> 1:1024.