Identifying subgroups and risk among frequent emergency department users in British Columbia.

: Frequent emergency department (ED) users are heterogeneous. We aimed to identify subgroups and assess their mortality. : We identified patients ≥18 years with ≥1 ED visit in British Columbia from April 1, 2012 to March 31, 2015, and linked to hospitalization, physician billing, prescription, and mortality data. Frequent users were the top 10% of patients by ED visits. We employed cluster analysis to identify frequent user subgroups. We assessed 365-day mortality using Kaplan-Meier curves and conducted Cox regressions to assess mortality risk factors within subgroups. : We identified 4 subgroups. Subgroup 1 ("Elderly") had median age 77 years (interquartile range [IQR]: 66-85), 5 visits/year (IQR: 4-6), median 8 prescription medications (IQR: 5-11), and 24.7% mortality. Subgroup 2 ("Mental Health and Alcohol Use") had median age 48 years (IQR: 34-61), 13 visits/year (IQR: 10-16), and 12.3% mortality. They made a median 31 general practitioner visits (IQR: 19-51); however, only 23.7% received a majority of services from 1 primary care physician. Subgroup 3 ("Young Mental Health") had median age 39 years (IQR: 28-51), 5 visits/year (IQR: 4-6), and 2.2% mortality. Subgroup 4 ("Short-term") had median age 50 years (IQR: 34-65), 4 visits/year (IQR: 4-5) regularly spaced over a short term, and 1.4% mortality. Male sex (all subgroups), long-term care ("Mental Health and Alcohol Use;" "Young Mental Health"), and rural residence ("Elderly" in long-term care; "Young Mental Health") were associated with increased mortality. : Our results identify frequent user subgroups with varying mortality. Future research should explore subgroups' unmet needs and tailor interventions toward them.