Subgroups of People Who Make Frequent Emergency Department Visits in Ontario and Alberta: a Retrospective Cohort Study.

Background: The population that visits emergency departments frequently is heterogeneous and at high risk for mortality. This study aimed to characterize these patients in Ontario and Alberta, compare them with controls who do not visit emergency departments frequently, and identify subgroups. Methods: This was a retrospective cohort study that captured patients in Ontario or Alberta from fiscal years 2011/12 to 2015/16 in the Dynamic Cohort from the Canadian Institute for Health Information, which defined people with frequent visits to the emergency department in the top 10% of annual visits and randomly selected controls from the bottom 90%. We included patients 18 years of age or older and linked to emergency department, hospitalization, continuing care, home care and mental health–related hospitalization data. We characterized people who made frequent visits to the emergency department over time, compared them with controls and identified subgroups using cluster analysis. We examined emergency department visit acuity using the Canadian Triage and Acuity Scale. Results: The number of patients who made frequent visits to the emergency department ranged from 435 334 to 477 647 each year in Ontario (≥ 4 visits per year), and from 98 840 to 105 047 in Alberta (≥ 5 visits per year). The acuity of these visits increased over time. Those who made frequent visits to the emergency department were older and used more health care services than controls. We identified 4 subgroups of those who made frequent visits: "short duration" (frequent, regularly spaced visits), "older patients" (median ages 69 and 64 years in Ontario and Alberta, respectively; more comorbidities; and more admissions), "young mental health" (median ages 45 and 40 years in Ontario and Alberta, respectively; and common mental health–related and alcohol-related visits) and "injury" (increased prevalence of injury-related visits). Interpretation: From 2011/12 to 2015/16, people who visited emergency departments frequently had increasing visit acuity, had higher health care use than controls, and comprised distinct subgroups. Emergency departments should codevelop interventions with the identified subgroups to address patient needs.