Lessons from COVID-19 Syndromic Surveillance Through Emergency Department Activity:  A Prospective Time-Series Study from Western Switzerland

Abstract

Background: Surveillance reports for COVID-19 use confirmed cases, deaths in the population and intensive care unit (ICU) occupancy, but emergency department (ED) syndromic surveillance is not routinely used. We aimed to assess if ED syndromic surveillance during the first and second waves of the COVID-19 outbreak could have improved our surveillance system. Methods: We did an observational study using aggregated data from the ED of a university hospital and public health authorities in western Switzerland. We used time series methods for ED syndromic surveillance and usual indicators from public health authorities. The relationship between ICU occupancy and surveillance indicators was explored by cross-correlation. We calculated the flu-like syndrome moving average and established Shewhart charts for aberration detection. Findings: Based on 37,319 ED visits during the COVID-19 outbreak, 1421 ED visits (3·8%) were positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Patients with flu-like syndrome or droplet isolation in the ED showed a similar correlation to ICU occupancy as confirmed cases in the general population with a time lag of approximately 13 days (0·73, 95% CI 0·64-0·80; 0·79, 95% CI 0·71-0·86; and 0·76, 95% CI 0·67-0·83, respectively). The proportion of positive tests in the population showed the best correlation with ICU occupancy (0·95, 95% CI 0·85-0·96). Interpretation: ED syndromic surveillance is an effective tool to detect and monitor a COVID-19 outbreak and to predict hospital resource needs, and would have allowed to anticipate ICU occupancy by 13 days, including detection of significant aberration at the beginning of the second wave. Funding Statement: The study had no funding. Declaration of Interests: We declare no competing interest. Ethics Approval Statement: This study was approved by the institutional ethics review board of the Canton of Vaud (CER-VD 2020-00731).