Evaluation of a SARS-CoV-2 rapid antigen test: Potential to help reduce community spread?

Abstract

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can spread from symptomatic patients with COVID-19, but also from asymptomatic individuals. Therefore, robust surveillance and timely interventions are essential for the control of virus spread within the community. In this regard the frequency of testing and speed of reporting, but not the test sensitivity alone, play a crucial role.

Objectives: In order to reduce the costs and meet the expanding demands in real-time RT-PCR (rRT-PCR) testing for SARS-CoV-2, complementary assays, such as rapid antigen tests, have been developed. Rigorous analysis under varying conditions is required to assess the clinical performance of these tests and to ensure reproducible results.

Results: We evaluated the sensitivity and specificity of a recently licensed rapid antigen test using 137 clinical samples in two institutions. Test sensitivity was between 88.2-89.6 % when applied to samples with viral loads typically seen in infectious patients. Of 32 rRT-PCR positive samples, 19 demonstrated infectivity in cell culture, and 84 % of these samples were reactive with the antigen test. Seven full-genome sequenced SARS-CoV-2 isolates and SARS-CoV-1 were detected with this antigen test, with no cross-reactivity against other common respiratory viruses.

Conclusions: Numerous antigen tests are available for SARS-CoV-2 testing and their performance to detect infectious individuals may vary. Head-to-head comparison along with cell culture testing for infectivity may prove useful to identify better performing antigen tests. The antigen test analyzed in this study is easy-to-use, inexpensive, and scalable. It can be helpful in monitoring infection trends and thus has potential to reduce transmission.

Keywords: Antigen test; Point-of-care testing; RT-PCR; SARS-CoV-2; Severe acute respiratory syndrome; Surveillance.

Fig. 1

Antigen test analysis performed in Berlin (A) and Frankfurt (B). A. Log₁₀ RNA copies/mL and corresponding antigen (Ag) detection test results (red circles positive n: 45, blue circles negative n: 13) for each rRT-PCR positive sample (n: 58). B. Cycle threshold (cT) value and corresponding antigen (Ag) detection test results (red circles positive n: 16, blue circles negative n: 16) for each rRT-PCR positive sample (n: 32). 32 rRT-PCR positive samples were tested in cell culture for infectivity. All Ag-test positive (n:16, red circles) and three Ag-test negative (red-filled blue circles) samples displayed CPEs after inoculating in Caco-2 cells (Table S2). Intensities of the test bands were compared to control band and designated as follows: +++ (test band intensity stronger than the control), ++ (test and control bans intensity are similar), + (test band intensity is weaker than the control).

Fig. 2

Rapid Antigen Test Results for SARS-CoV-1 and SARS-CoV-2 isolates. A. Representative lateral flow assay using serially diluted virus stocks. Intensities of the test bands were compared to control band and designated as follows: +++ (test band intensity stronger than the control), ++ (test and control bans intensity are similar), + (test band intensity is weaker than the control). B. TCID50/mL values and corresponding antigen (Ag) detection test intensity for serially diluted SARS-CoV-2 isolates FFM1-7 and SARS-CoV-1 are shown. Representative result of two experiments.