Seroconversion in newly diagnosed cases of coronavirus disease

Abstract

Objective: To determine the percentage of seroconverted real time reverse transcriptase polymerase chain reaction (RT-PCR) positive coronavirus disease (COVID-19) cases at different days post-symptom onset; and also find the agreement of chemiluminescence assay used for total antibody detection using RT-PCR as a reference method. Study Design: Cross-sectional study. Place and Duration of Study: Chughtai Institute of Pathology from April to May 2020. Methodology: Fifty pre-pandemic samples (healthy population) and 75 COVID-19 patients were included in the study. RT-PCR confirmed COVID-19 patients were divided into 3 equal groups (25 each), according to the days of symptom onset. The samples were analysed using electro-chemiluminescence as assay principle. Positive and negative agreement of COVID-19 antibodies was calculated using EP evaluator to find out the sensitivity of chemiluminescence assay for total antibody detection. The results were analysed using SPSS version 23.0. Results: All the pre-pandemic samples tested were negative for antibodies with a negative agreement of 100%. Total agreement at day 7 post-symptom onset was 84%; whereas, it was 94% at day 14 and increased rapidly to 100% at day 21 postsymptom onset. At day 7 post-symptom onset, 68% of patients were seroconverted; and this percentage was 88% and 100% at day 14 and 21 post-symptom onset, respectively. Conclusion: Pre-pandemic samples were non-reactive for COVID-19 antibodies and seroconversion started within the first week post-virus exposure. There was 100% concordance between RT-PCR result and antibody positivity 21 days post-symptom onset.