RESUMO
ImportanceLongitudinal 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. ObjectiveTo 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. DesignRepeated cross-sectional, diagnostic accuracy study performed prospectively in the field. SettingBusinesses in Montreal, Quebec, Canada, with at least 2 active cases of SARS-CoV-2 infection. ParticipantsUntrained, asymptomatic persons in their workplace, not meeting Public Health quarantine criteria. ExposuresA Modified Quick Reference Guide compared to the original manufacturers 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. ResultsOverall, 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 RelevanceLongitudinal 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 PointsO_ST_ABSQuestioC_ST_ABSDo untrained users correctly perform and interpret the results of SARS-CoV-2 rapid antigen detection tests (RADT) in the workplace, and how can their performance be optimised? FindingsIn this prospective field evaluation of self-performed SARS-CoV-2 RADT in an intended-use setting, we found that the accuracy of RADT interpretation was poor when the manufacturers instructions were used. A Modified Quick Reference Guide yielded significantly better user performance. MeaningLongitudinal 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.
RESUMO
BACKGROUNDEssential workers are at increased risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We did a prospective study to estimate the yield, acceptability, and costs of workplace-based systematic SARS-CoV-2 testing of asymptomatic essential workers. METHODSWe recruited non-healthcare essential businesses, in Montreal, Canada. Mobile teams, composed of two non-healthcare professionals each, visited businesses. Consenting, asymptomatic employees provided saline gargle specimens under supervision. Mobile team members self-sampled weekly. Specimens were analyzed using reverse-transcription polymerase chain reaction (RT-PCR). If an outbreak was detected ([≥]2 positives), we retested all initially negative participants. We did logistic regression for factors associated with a positive test. We estimated costs ($CAD) of this strategy. RESULTSFrom 27 January to 12 March 2021, 69 essential businesses were visited. Of an estimated 2348 employees onsite, 2128 (90.6%) participated. Across 2626 tests, 53 (2.0%) were positive. Self-reported non-Caucasian ethnicity (aOR 3.7, 95% CI: 1.4-9.9) and a negative SARS-CoV-2 test before the study (0.4, 0.2-0.8) were positively and negatively associated with a positive test, respectively. Five businesses--3 manufacturing/supplier and 2 meat processing-- were experiencing an outbreak. At these businesses, 40 (4.4%) of 917 participants were positive on the initial test. We repeated testing at three of these businesses over 2-3 weeks: 8/350 (2.3%) were positive on the second test, and zero were positive on the third and fourth test (148 tests); no employer reported new positives to 26 March 2021. In all other businesses, 1211 participants were tested once--5 (0.4%) were positive at three childcare enterprises, one grocery store, and one manufacturing/supplier. Per person, RT-PCR costs were $34.00 and all other costs $8.67. No mobile team member tested positive. INTERPRETATIONOnsite sampling of essential workers with saline gargle is safe, acceptable, and inexpensive. Repeat testing appeared to eliminate outbreaks. Systematic testing should be considered part of SARS-CoV-2 preventive efforts.
