Systematic Testing for SARS-CoV-2 Infection Among Essential Workers in Montreal, Canada: A Prospective Observational and Cost Assessment Study

Campbell, J. R.; Dion, C.; Uppal, A.; Yansouni, C. P.; Menzies, D.

BACKGROUND: Essential 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. METHODS: We 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. RESULTS: From 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. INTERPRETATION: Onsite 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.