Systematic on-site testing for SARS-CoV-2 infection among asymptomatic essential workers in Montréal, Canada: a prospective observational and cost-assessment study

Abstract

Background: Essential workers are at increased risk for SARS-CoV-2 infection. We aimed to estimate the yield, acceptability and cost of systematic workplace-based testing of asymptomatic essential workers for SARS-CoV-2 infection. Methods: From Jan. 27 to Mar. 12, 2021, we prospectively recruited non–health care essential businesses in Montréal, Canada, through email or telephone contact. Two trained mobile teams, each composed of 2 non–health care professionals, visited businesses. Consenting asymptomatic employees provided saline gargle samples under supervision. Samples were analyzed by means of reverse transcription polymerase chain reaction (RT-PCR). At businesses with outbreaks (≥ 2 participants with a positive result), we retested all participants with a negative result on initial testing. Our primary outcomes were yield (proportion of test results that were positive), acceptability (proportion of participants estimated to be present at the business who agreed to participate) and costs (including training, sample collection and analysis, and communicating results). Our secondary outcome was identification of factors associated with a positive test result on multivariable logistic regression. Results: Of the 366 businesses contacted, 69 (18.8%) agreed to participate. Nineteen businesses (28%) were manufacturers or suppliers, 12 (17%) were in auto sales or repair, and 11 (16%) were in childcare; the corresponding number of employees was 1225, 242 and 113. The median number of participants per business was 13 (interquartile range [IQR] 8–22). Of an estimated 2348 employees on site, 2128 (90.6%) participated (808 [38.0%] female, median age 48 [IQR 37–57] yr). Of the 2626 tests performed, 53 (2.0%) gave a positive result. Self-reported nonwhite ethnicity (adjusted odds ratio [OR] 3.7, 95% confidence interval [CI] 1.4–9.9) and a negative SARS-CoV-2 test result before the study (adjusted OR 0.4, 95% CI 0.2–0.8) were associated with a positive test result. Five businesses were experiencing an outbreak; at these businesses, 40/917 participants (4.4%) had a positive result on the initial test. We repeated testing for employees with initially negative results at 3 of these businesses over 2–3 weeks: 8/350 participants (2.3%) had a positive result on the second test, and none had a positive result on the third and fourth tests; no employer reported new positive results after our final visit (up to Mar. 26, 2021). At the remaining 64 businesses, 1211 participants were tested once, of whom 5 (0.4%) had a positive result. The per-person RT-PCR cost was $34, and all other costs, $8.67. Interpretation: On-site saline gargle sampling of essential workers for SARS-CoV-2 testing was acceptable and of modest cost, and appears most useful in the context of outbreaks. This sampling strategy should be evaluated further as a component of efforts to prevent SARS-CoV-2 transmission. Preprint: medRxiv —...

Characteristics associated with SARS-CoV-2 testing, infection and vaccine uptake among essential non-healthcare workers in Montréal, 2021

“…Identical questionnaires were used in both studies except for additional questions related to vaccination in the Self-Testing Study, Appendix 1 , Supplemental material . Detailed descriptions of the individual studies are available elsewhere ( 8 , 9 ).…”

“…We performed logistic regression with generalized linear mixed models to estimate the adjusted odds ratio (aOR) and 95% confidence interval (CI) for each outcome, with the business sector treated as a random intercept. Models included weakly informative priors to deal with quasi-complete separation of some fixed effects observed in previous studies ( 8 ). Models were adjusted for individual and business characteristics as well as the study (to determine differences in risk between studies), as appropriate.…”

“…In 2021, we conducted two studies among non-healthcare essential workers in Montréal, Canada. In the first study, we visited businesses to assess onsite sampling for SARS-CoV-2 testing from January to March 2021 ( 8 ); a period with substantial public health measures to curb SARS-CoV-2 transmission and prior to the wide availability of SARS-CoV-2 vaccines. In the second study, we evaluated self-testing for SARS-CoV-2 with rapid diagnostic tests in similar businesses, from July to October 2021 ( 9 ); a period with minimal public health measures in effect and after all adults were eligible for SARS-CoV-2 vaccination ( 10 ).…”

Adequacy of Serial Self-performed SARS-CoV-2 Rapid Antigen Detection Testing for Longitudinal Mass Screening in the Workplace

“…Businesses with newly identified outbreaks were contacted by the study team by telephone and offered participation in the study via the deployment of 1 of 4 mobile teams on-site. Among outbreak businesses, priority was given to contacting those with greater than 50 employees to increase the probability of identifying participants with unsuspected SARS-CoV-2 infection . For businesses that agreed to participate, study visits were scheduled twice weekly for 2 weeks (4 visits).…”