COVID-19(13) 95% confidence interval(12) Emergency(10) Infection(9) 95% CI(9) Department(8) COVID-19 pandemic(8) age(7) identify(6) SARS-CoV-2(6) increase in(6) SARS-COV-2 infection(6) performed(6) prospective cohort study(6) Patient(5) evaluate(5) conducted(5) emergency department(5) hospital(5) subgroups(4) Elecsys(4) Seroprevalence(4) demonstrated(4) Blood donors(4) Matched(4) paramedics(4) evidence of(4) Secondary analyses(4) antibody(4) risk(4)