Diagnostic performance and clinical implications of rapid SARS-CoV-2 antigen testing in Mexico using real-world nationwide COVID-19 registry data

Abstract

BACKGROUNDSARS-CoV-2 testing capacity is important to monitor epidemic dynamics. Given difficulties of large-scale RT-PCR implementation, rapid antigen tests (Rapid Ag-T) have been proposed as alternatives in settings such as Mexico.OBJECTIVESTo evaluate diagnostic performance of Rapid Ag-T for SARS-CoV-2 infection and its associated clinical implications compared to RT-PCR testing in Mexico.METHODSWe analyzed data from the COVID-19 registry of the Mexican General Directorate of Epidemiology up to December 31st, 2020 (n=3,374,165) and cases with both RT-PCR and Rapid Ag-T (n=18,446). We evaluated diagnostic performance using accuracy measures and assessed time-dependent changes in AUROC. We also explored test discordances as predictors of hospitalization, intubation, severe COVID-19 and mortality.RESULTSRapid Ag-T is primarily used in Mexico City. Rapid Ag-T have low sensitivity 37.6% (95%CI 36.6-38.7), high specificity 95.4% (95%CI 95.1-95.8) and acceptable positive 86.1% (95%CI 85.0-86.6) and negative predictive values 67.2% (95%CI 66.2-69.2). Rapid Ag-T has optimal diagnostic performance up to days 7-10 after symptom, and its performance is modified by testing location, comorbidity, and age. RT-PCR(-) / Rapid Ag-T(+) cases had higher risk of adverse COVID-19 outcomes and were older, RT-PCR(+)/ Rapid Ag-T(-) cases had slightly higher risk or adverse outcomes and ≥7 days from symptom onset. Cases detected with rapid Ag-T were younger, without comorbidities, and milder COVID-19 course.CONCLUSIONSRapid Ag-T could be used as an alternative to RT-PCR for large scale SARS-CoV-2 testing in Mexico. Interpretation of Rapid Ag-T results should be done with caution to minimize the risk associated with false negative results.

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