Analytical sensitivity of COVID-19 rapid antigen tests: A case for a robust reference standard

Diagnostic performance of multiplex lateral flow tests in ambulatory patients with acute respiratory illness

We assessed the performance of three different multiplex lateral flow assays manufactured by SureScreen, Microprofit and Goldsite which provide results for influenza, respiratory syncytial virus (RSV) and SARS-CoV-2. Between 4 April and 20 October 2023, 1646 patients 6 months and older presenting to an outpatient department of a hospital in Hong Kong with ≥2 symptoms or signs of an acute respiratory illness were enrolled. The point estimates for all three multiplex tests had sensitivity >80% for influenza A and SARS-CoV-2 compared to PCR, and the tests manufactured by Microprofit and Goldsite had sensitivity >84% to detect RSV. Specificity was >97% for all three tests except for the SureScreen test which had specificity 86.2% (95% CI: 83.9% to 88.3%) for influenza A. Sensitivity was lower than reported by the manufacturers, resulting in a higher risk of false negatives. The three multiplex tests performed better in patients with high viral loads.

Comparison of the analytical sensitivity of COVID-19 rapid antigen tests in Australia and Canada

Rapid testing has become an indispensable strategy to identify the most infectious individuals and prevent the transmission of SARS-CoV-2 in vulnerable populations. As such, COVID-19 rapid antigen tests (RATs) are being manufactured faster than ever yet lack relevant comparative analyses required to inform on absolute analytical sensitivity and performance, limiting end-user ability to accurately compare brands for decision making. To date, more than 1000 different COVID-19 RATs are commercially available in the world, most of which detect the viral nucleocapsid protein (NP). Here, we examine and compare the analytical sensitivity of 26 RATs that are readily available in Canada and/or Australia using two NP reference materials (RMs) - a fluorescent NP-GFP expressed in bacterial cells and NCAP-1 produced in a mammalian expression system. Both RMs generate highly comparable results within each RAT, indicating minimal bias due to differing expression systems and final buffer compositions. However, we demonstrate orders of magnitude differences in analytical sensitivities among distinct RATs, and find little correlation with the median tissue culture infectious dose (TCID50) assay values reported by manufacturers. In addition, two COVID-19/Influenza A&B combination RATs were evaluated with influenza A NP-GFP. Finally, important logistics considerations are discussed regarding the robustness, ease of international shipping and safe use of these reference proteins. Taken together, our data highlight the need for and practicality of readily available, reliable reference proteins for end-users that will ensure that manufacturers maintain batch-to-batch quality and accuracy of RATs. They will aid international public health and government agencies, as well as health and aged care facilities to reliably benchmark and select the best RATs to curb transmission of future SARS-CoV-2 and influenza outbreaks.

The Suitability of RNA from Positive SARS-CoV-2 Rapid Antigen Tests for Whole Virus Genome Sequencing and Variant Identification to Maintain Genomic Surveillance

The COVID-19 pandemic has transformed laboratory management, with a surge in demand for diagnostic tests prompting the adoption of new diagnostic assays and the spread of variant surveillance tools. Rapid antigen tests (RATs) were initially used only for screening and later as suitable infection assessment tools. This study explores the feasibility of sequencing the SARS-CoV-2 genome from the residue of the nasopharyngeal swab extraction buffers of rapid antigen tests (RATs) to identify different COVID-19 lineages and sub-lineages.

METHODS

Viral RNA was extracted from the residue of the nasopharyngeal swab extraction buffers of RATs and, after a confirmation of positivity through a reaction of RT-PCR, viral genome sequencing was performed.

RESULTS

Overall, the quality of the sequences obtained from the RNA extracted from the residue of the nasopharyngeal swab extraction buffers of RATs was adequate and allowed us to identify the SARS-CoV-2 variants' circulation and distribution in a period when the use of molecular swabs had been drastically reduced.

CONCLUSIONS

This study demonstrates the potential for genomic surveillance by sequencing SARS-CoV-2 from the residue of the nasopharyngeal swab extraction buffers of RATs, highlighting alternative possibilities for tracking variants.