The Performance of the manual and Sofia rapid antigen test in medical staff exposed to Omicron variants

Background: Variable COVID-19 rapid antigen test sensitivity had been reported and the effect of viral variants focus the attention due to impact in the early detection of cases. Objective: To compare the performance of antigen tests (manual RAT, and Sofia test) in medical staff exposed during the circulation periods of different Omicron variants. Methods: Descriptive study of samples collected for the diagnosis of SARS-CoV-2 infection in medical staff at TCH Hospital from December 2021 to December 2022, including cases confirmed by SARS CoV-2 PCR, and a RAT. Dec 2021 - March 2022 and June-Dec 2022 were considered the periods of Omicron BA.1.1. variants and Omicron BA.4/5 respectively. Comparison of Ct figures between categories was carried out using the Wilcoxon-Mann-Whitney test, and sensitivity (95% confidence intervals) were calculated. Results: 287 healthcare workers were confirmed with COVID-19 during the study period, 56.1% during B.1.1. variant period, and 43.9% during B.4/5 variants predominant circulation. Sensitivity of the manual RAT test (82.5%; 95% CI 73.4 - 89.4) was higher during B.1.1. variant circulation in comparison with the B.4/5 period (68.9%;53.4-81.8). These two methods during this B.4/5 period had quite similar sensitivity figures when compared to each other; manual 68.9% (95% CI 53.4 - 81.8) and Sofia 72.7% (95% CI 60.4 - 83.0). Conclusion: The variation in sensitivity of the RAT for SARS CoV-2 variants and the similar performance of manual and SOFIA methods of RAT could be considered in the diagnostic approach of COVID-19 and the appropriate isolation of potentially infectious cases.