Adequacy of serial self-performed SARS-CoV-2 rapid antigen-detection testing for longitudinal mass screening in the workplace

Importance

Longitudinal mass testing using rapid antigen detection tests (RADT) for serial screening of asymptomatic persons has been proposed for preventing SARS-CoV-2 community transmission. The feasibility of this strategy relies on implementation of accurate self-performed RADT testing where people live, work, or attend school.

Objective

To quantify the adequacy of serial self-performed SARS-CoV-2 RADT testing in the workplace, in terms of the frequency of correct execution of procedural steps and accurate interpretation of the range of possible RADT results. We compared results using the instructions provided by the manufacturer to those with modified instructions that were informed by the most frequent or most critical errors we observed.

Design

Repeated cross-sectional, diagnostic accuracy study performed prospectively in the field.

Setting

Businesses in Montreal, Quebec, Canada, with at least 2 active cases of SARS-CoV-2 infection.

Participants

Untrained, asymptomatic persons in their workplace, not meeting Public Health quarantine criteria.

Exposures

A Modified Quick Reference Guide compared to the original manufacturer’s instructions.

Main Outcome(s) and Measure(s)

The difference in the proportions of correctly performed procedural steps, and the difference in proportions of correctly interpreted RADT proficiency panel results. The secondary outcome, among subjects with two self-testing visits, compared the second to the first self-test visit using the same measures.

Results

Overall, 1892 tests were performed among 647 subjects. For self-test visit 1, significantly better accuracy in test interpretation was observed using the Modified Quick Reference Guide for weak positive (55.6% vs. 12.3%; 43.3 percentage point improvement, 95% confidence interval [CI] 33.0%-53.8%), positive (89.6% vs. 51.5%; 38.1% difference, 95%CI 28.5%-47.5%), strong positive (95.6% vs. 84.0%; 11.6% improvement, 95%CI 6.8%-16.3%) and invalid (87.3% vs. 77.3%; 10.0% improvement, 95%CI 3.8%-16.3%) tests. Use of the modified guide was associated with smaller, statistically significant, improvements on self-test visit 2. For procedural steps identified as critical for the validity of test results, adherence to procedural testing steps did not differ meaningfully according to instructions provided or reader experience.

Conclusions and Relevance

Longitudinal mass RADT testing for SARS-CoV-2 can be accurately self-performed in an intended-use setting; this work provides evidence for how to optimise performance.

Key Points