Frequent users of Hospital Emergency Departments: Who, what, when, where and why

Frequent users of hospital emergency departments (ED) have long been a focal group for health practitioners and delivery systems, and increasingly are of interest to policymakers as they seek cost-containing strategies for publicly-insured patients. Current literature is limited by its cross-sectional nature or single hospital focus; fewer studies track patients over time and across an entire state as large and diverse as California. We use non-public California hospital discharge data to construct a patient-level dataset that includes detailed information on the universe of ED encounters between 2009 and 2011. We examine variations in patient demographic (age, gender, race/ethnicity, insurance coverage, language) and health characteristics by frequency of ED use.  We perform both bi-variate and multi-variate analysis to identify correlates associated with frequent users and test multiple definitions of frequent use. Our findings indicate that a small percentage of patients are responsible for a considerable volume of all ED visits.  Less than one percent of patients are responsible for more than 10% of all ED visits, while 8% of patients account for nearly one-third.  In addition, patients who report Medicaid coverage for all or some visits and those with identified mental health or substance use conditions have higher likelihoods (OR 3.1, 2.2, respectively) of being a frequent user. As millions gain coverage under the Affordable Care Act, many through state Medicaid programs, it will be essential to better manage the care of patients who consume considerable resources and a better understanding of heavy ED users can help target those efforts.