Risk of SARS-CoV-2 among Ontario Healthcare Workers: A comparison of test-negative and cohort study designs in a heterogeneous reason-for-testing population.

Everest, Louis; Demers, Paul A; Smith, Brendan T; Kim, JinHee; Arrandale, Victoria H; Harris, M Anne; Song, Chaojie; Kirkham, Tracy L et al. · J Occup Environ Med · 2026

retrospective_cohort · Level III

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Abstract

Differential reason-for-testing may bias test-negative estimates. This study aimed to estimate healthcare worker SARS-CoV-2 risk, with adjustment for healthcare seeking behaviour and unmeasured reason-for-testing. 1.2-million workers in Ontario, Canada were followed for SARS-CoV-2 PCR tests from February 2020 to December 2021. Hazard ratios (HR) were used to estimate SARS-CoV-2 risk in healthcare workers versus non-healthcare workers based on the overall and test-negative sub-cohort. Unmeasured reason-for-testing was examined through probabilistic-bias-analyses. In the test-negative sub-cohort, healthcare and non-healthcare workers had similar risk of SARS-CoV-2. However, healthcare workers had an increased risk in the symptomatic-adjusted (HR: 1.15, 95% CI 1.03-1.40) and asymptomatic-adjusted (HR: 2.83, 95% CI: 1.08-9.07) models. Future test-negative studies should account for potential bias from varying symptomatic and asymptomatic testing groups and may consider using probabilistic-bias-analysis methods when reason-for-testing data is missing.