Evaluation and Revision of Historical ESSENCE Syndromic Surveillance Definition Used to Identify Work-Related Emergency Department Visits

Objectives: Occupational health surveillance programs have rarely incorporated syndromic surveillance. We documented a process for evaluating and revising syndromic surveillance definitions, using the example of work-related emergency department (ED) visits.Materials and Methods: Of 140 331 481 ED visits in the National Syndromic Surveillance Program from May 15, 2016, through October 31, 2017, we extracted 391 827 records for phase 1 that met the previously unevaluated original work-related definition or included a work-related employment status ICD-10-CM code (Y99.0/Y99.1; International Classification of Diseases, Tenth Revision, Clinical Modification). Also for phase 1, we evaluated the performance of the original work-related definition using ICD-10-CM work-related employment status codes as a reference standard. In phase 2, we extracted 99 109 records containing candidate work-related keywords. Finally, in phase 3, we examined individual keywords and developed and evaluated a revised definition.Results: The revised work-related definition identified 259 153 visits by keyword alone, 104 342 visits by ICD-10-CM work-related employment status codes alone, and 16 385 ED visits by both methods. Sensitivity (13.6% vs 11.3%) and positive predictive value (5.9% vs 4.8%) were higher for the revised definition than for the original work-related definition. Manual review indicated that 91.3% (95% CI, 89.6%-93.0%) of visits identified by the revised definition keywords met the study criteria for work-related visits as compared with 75.5% (95% CI, 73.0%-78.4%) of visits for the original work-related definition.Practice Implications: The original work-related definition performed suboptimally because keywords were not sufficiently specific. The revised definition is an improvement but requires testing in real-world scenarios. The presented methods for developing a syndromic surveillance definition are useful, not only for occupational health, but for identification of other subpopulations treated in the ED.