Can variants, reinfection, symptoms and test types affect COVID-19 diagnostic performance? A large-scale retrospective study of AG-RDTs during circulation of Delta and Omicron variants, Czechia, December 2021 to February 2022

Abstract

Background The sensitivity and specificity of selected antigen detection rapid diagnostic tests (AG-RDTs) for SARS-CoV-2 were determined in the unvaccinated population when the Delta variant was circulating. Viral loads, dynamics, symptoms and tissue tropism differ between Omicron and Delta. Aim We aimed to compare AG-RDT sensitivity and specificity in selected subgroups during Omicron vs Delta circulation. Methods We retrospectively paired AG-RDT results with PCRs registered in Czechia’s Information System for Infectious Diseases from 1 to 25 December 2021 (Delta, n = 20,121) and 20 January to 24 February 2022 (Omicron, n = 47,104). Results When confirmatory PCR was conducted on the same day as AG-RDT as a proxy for antigen testing close to peak viral load, the average sensitivity for Delta was 80.4% and for Omicron 81.4% (p < 0.05). Sensitivity in vaccinated individuals was lower for Omicron (OR = 0.94; 95% confidence interval (CI): 0.87–1.03), particularly in reinfections (OR = 0.83; 95% CI: 0.75–0.92). Saliva AG-RDT sensitivity was below average for both Delta (74.4%) and Omicron (78.4%). Tests on the European Union Category A list had higher sensitivity than tests in Category B. The highest sensitivity for Omicron (88.5%) was recorded for patients with loss of smell or taste, however, these symptoms were almost 10-fold less common than for Delta. The sensitivity of AG-RDTs performed on initially asymptomatic individuals done 1, 2 or 3 days before a positive PCR test was consistently lower for Omicron compared with Delta. Conclusion Sensitivity for Omicron was lower in subgroups that may become more common if SARS-CoV-2 becomes an endemic virus.

Developing molecular surveillance of SARS-CoV-2 in the Czech Republic (2021–2022)

“…Participation in in-person voting during the October 2021 general election may have also accelerated the rate of confirmed infections and hospital admissions [21]. The observed dominance of the Delta variant in the November 2021 wave has been attributed to waning vaccine-induced immunity combined with the novel antigenic profile of the Delta variant, resulting in increasing vaccine breakthrough infections [22,23]. Throughout the pandemic, excess mortality in the Czech Republic was similar to that in neighbouring central European countries, however, the rates of excess mortality in central Europe were some of the highest in the world [24].…”

Diagnostic performance of rapid antigen tests (RAT) for COVID-19 and factors associated with RAT-negative results among RT-PCR-positive individuals during Omicron BA.2, BA.5 and XBB.1 predominance

“…Data on the effect of reinfection on the performance of RATs remain limited. A Czechia study reported that RAT sensitivity for Omicron cases with a previous infection was 79.2% (95% confidence interval [CI] 77.8–80.5%) compared with 81.9% (95% CI 81.3–82.5%) for those without a confirmed previous infection, but the study was conducted during the early Omicron period with data up to February 2022 [ 13 ].…”