Clinical Evaluation of Roche SD Biosensor Rapid Antigen Test for SARS-CoV-2

Testing Site Setup and the Mobile Laboratory

From the 6 available testing posts, we designated 2 posts for sample collection from study participant on the basis of 3 factors: maximum number of subjects per test post (≈150/day); known number of appointments per day; and expected enrollment rate based on initial results from other study sites in the Netherlands. We expected to include a maximum of 300 persons/day. The site’s regular trained personnel performed swabbing to avoid variations to the process. Testing was done on benchtop, in a mobile laboratory unit by trained staff dressed in full personal protective equipment (goggles, FFP3 mask, gloves, and disposable gown). Samples for the Ag RDT were collected at regular intervals and processed as soon as possible within 30 mins in convenient batches (5–10 tests at a time). Swab specimens and RDT devices were inactivated in chlorine and disposed of as biohazard material. Results were recorded in a Microsoft Access database designated for this study.

Specimen Collection, Testing and Culture Procedures

Standard method for SARS-CoV-2 testing was by RT-PCR, which was conducted in parallel with the Ag RDT on separate swab specimens. Two swab specimens (1 oropharyngeal and 1 nasopharyngeal swab) were taken for RT-PCR and virus culture, placed directly in 3 mL universal transport media and shipped to the Erasmus MC viroscience diagnostic laboratory (Rotterdam, the Netherlands). For the Ag RDT evaluation, a second nasopharyngeal swab specimen was taken from the same nostril, using the swab included in the kits, to directly compare RT-PCR results with Ag RDT results.

Swabs were placed into empty tubes to transport to the mobile laboratory onsite. Routine RT-PCR testing was performed on combined oropharyngeal and one nasopharyngeal swabs in virus transport medium using the cobas SARS-CoV-2 test on the COBAS6800 (Roche Diagnostics). Because cycle threshold (C_t) values differ between PCR methods, genome copies per milliliter were calculated based on an in-house established standard curve. The leftover virus transport medium from the oropharyngeal and nasopharyngeal swabs was directly inoculated onto Vero cells clone 118 without freezing or extended storage. Samples were cultured for 7 days; once cytopathic effect was visible, the presence of SARS-CoV-2 was confirmed with immunofluorescent detection of SARS CoV-2 nucleocapsid protein.

For the Ag RDT, the SD Biosensor SARS-CoV-2 rapid antigen test distributed by Roche (reference no. 9901-NCOV-01G; lot no. QCO3020079/Sub:A-2) was performed immediately onsite following manufacturer’s instructions. A 4-grade scaling readout (−; +/−, +; ++) representing the strength of the test band was used . Time until positive results was logged as <5 min, <10 min (not part of the manufacturer’s instructions for use), or 15 min; recommended readout was 15–30 min. When results were dubious (i.e., test line barely visible or labeled as +/− but regarded as positive test result), 2 persons performed the readout.

Data Analysis

We merged data from the Ag RDT, RT-PCR, virus culture, and clinical questionnaire using Microsoft Access and data performed analysis using R version 4.0.2 . Sensitivity and specificity of Ag RDT were calculated in relation to the RT-PCR results. Wilcoxon score interval was used to determine CIs of proportions.

Rapid detection of infection is essential for stopping the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The Roche SD Biosensor rapid antigen test for SARS-CoV-2 was evaluated in a nonhospitalized symptomatic population. We rapid-tested a sample onsite and compared results with those from reverse transcription PCR and virus culture. We analyzed date of onset and symptoms using data from a clinical questionnaire.

Overall test sensitivity was 84.9% (95% CI 79.1–89.4) and specificity was 99.5% (95% CI 98.7–99.8). Sensitivity increased to 95.8% (95% CI 90.5–98.2) for persons who sought care within 7 days of symptom onset. Test band intensity and time to result correlated strongly with viral load; thus, strong positive results could be read before the recommended time. Approximately 98% of all viable specimens with cycle threshold <30 were detected. Rapid antigen tests can detect symptomatic  infections in the early phase of disease, thereby identifying the most infectious persons.