Multicentre diagnostic evaluation of OnSite COVID-19 Rapid Test (CTK Biotech) among symptomatic individuals in Brazil and The United Kingdom

The COVID-19 pandemic has given rise to numerous commercially available antigen rapid diagnostic tests (Ag-RDTs). To generate and share accurate and independent data with the global community, multi-site prospective diagnostic evaluations of Ag-RDTs are required. This report describes the clinical evaluation of OnSite COVID-19 Rapid Test (CTK Biotech, California, USA) in Brazil and The United Kingdom. A total of 496 paired nasopharyngeal (NP) swabs were collected from symptomatic healthcare workers at Hospital das Clinicas in Sao Paulo, and 211 NP swabs were collected from symptomatic participants at a COVID-19 drive-through testing site in Liverpool, England. These swabs were analysed by Ag-RDT and results were compared to RT-qPCR. The clinical sensitivity of the OnSite COVID-19 Rapid test in Brazil was 90.3% [95% Cl 75.1 - 96.7%] and in the United Kingdom was 75.3% [95% Cl 64.6 - 83.6%]. The clinical specificity in Brazil was 99.4% [95% Cl 98.1 - 99.8%] and in the United Kingdom was 95.5% [95% Cl 90.6 - 97.9%]. Analytical evaluation of the Ag-RDT was assessed using direct culture supernatant of SARS-CoV-2 strains from Wild-Type (WT), Alpha, Delta, Gamma and Omicron lineages. Analytical limit of detection was 1.0x103 pfu/mL, 1.0x103 pfu/mL, 1.0x102 pfu/mL, 5.0x103 pfu/mL and 1.0x103 pfu/mL, giving a viral copy equivalent of approximately 2.1x105 copies/mL, 2.1x104 copies/mL, 1.6x104 copies/mL, 3.5x106 copies/mL and 8.7 x 104 for the Ag-RDT, when tested on the WT, Alpha, Delta, Gamma and Omicron lineages, respectively. This study provides comparative performance of an Ag-RDT across two different settings, geographical areas, and population. Overall, the OnSite Ag-RDT demonstrated a lower clinical sensitivity than claimed by the manufacturer... Sensitivity and specificity from the Brazil study fulfilled the performance criteria determined by the World Health Organisation but the performance obtained from the UK study failed to. Further evaluation of the use of Ag-RDTs should include harmonised protocols between laboratories to facilitate comparison between settings.