Electronic Syndromic Surveillance for Influenza-like Illness in Different Treatment Settings
Background: Syndromic surveillance in an epidemiologic tool that utilizes near "real-time" clinical data to track disease. Currently, most syndromic surveillance for influenza-like illness (ILI) is performed using outpatient data. As hospitals adopt electronic health records, more electronic data will be available from different treatment settings for syndromic surveillance. It is not known how to best utilize this data to monitor ILI in different treatment settings (e.g. Emergency Department (ED), outpatient, and inpatient).
Methods: We conducted a retrospective cohort study in a 4-hospital health system. All inpatient encounters, ED encounters, and outpatient primary care encounters from January 1, 2006 through May 31, 2013 were included. We applied an ILI syndromic surveillance algorithm that was previously validated in the outpatient setting to the ED and inpatient settings (Figure 1). Using the algorithm to query the Enterprise Data Warehouse (EDW), we calculated the percentage of encounters for ILI per week in each treatment setting. We compared results from different treatment settings using Pearson correlation coefficient.
Results: Over the study period, there were 3,443,913 outpatient visits, 393,835 inpatient encounters, and 610,002 ED encounters. ED algorithm results correlated closely with outpatient results (rho=0.875), but inpatient algorithm results were less similar (rho=0.375) (Figure 2). During the time period when H1N1 was circulating (April 2009-March 2010), outpatient-ED correlation was 0.8617 and outpatient-inpatient correlation was 0.6676. Correlation between outpatient and ED algorithm results was stronger among patients less than18 years old than among those over age 65 (rho=0.79 vs. 0.44). The seasonal uptick in ILI encounters for patients < 18 years old preceded the rise for older patients in the outpatient setting (Figure 3) and for children in other settings.
Conclusion: Data streams from the outpatient and ED settings provide similar syndromic surveillance information regarding ILI activity, whereas inpatient ILI data is less similar. Children in the outpatient setting see a seasonal rise in ILI activity before adults and children in other settings.
J. P. Ridgway,
A. Robicsek, None