Sample size calculation
The estimate of the sample size was based on the comparison of 2 proportions under individual randomization using Fisher’s exact test, with 0.1% of newly diagnosed SARS-CoV-2–positive patients among the included patients (control) and 0.2% (intervention), with a 2-sided significance, α = 5%, and β = 10%. Taking the intracluster (rho = 0.00014) and between-cluster (rho12 = 0.00009) correlations previously estimated [The proportion of the control group was based on the incidence rate of 0.12% in the Paris metropolitan region on 26/11/2020. It was estimated that the proportion of 0.10% was close to the baseline proportion of new diagnoses among ED patients with routine screening. Simulations were performed using different incidence rates; the worst-case scenario involving the largest number of patients to be included was selected. The calculation was performed by an independent biostatistician with SAS software (version 9.4; SAS Institute, Cary, North Carolina, United States of America).