title: Rates of Mental Illness and Addiction among High-Cost Users of Medical Services in Ontario.
abstract: To quantify the burden of mental illness and addiction among high-costing users of medical services (HCUs) using population-level data from Ontario, and compare to a referent group of nonusers.
  
  
  
  We conducted a population-level cohort study using health administrative data from fiscal year 2011-2012 for all Ontarians with valid health insurance as of April 1, 2011 (N = 10,909,351). Individuals were grouped based on medical costs for hospital, emergency, home, complex continuing, and rehabilitation care in 2011-2012: top 1%, top 2% to 5%, top 6% to 50%, bottom 50%, and a zero-cost nonuser group. The rate of diagnosed psychotic, major mood, and substance use disorders in each group was compared to the zero-cost referent group with adjusted odds ratios (AORs) for age, sex, and socioeconomic status. A sensitivity analysis included anxiety and other disorders.
  
  
  
  Mental illness and addiction rates increased across cost groups affecting 17.0% of the top 1% of users versus 5.7% of the zero-cost group (AOR, 3.70; 95% confidence interval [CI], 3.59 to 3.81). This finding was most pronounced for psychotic disorders (3.7% vs. 0.7%; AOR, 5.07; 95% CI, 4.77 to 5.38) and persisted for mood disorders (10.0% vs. 3.3%; AOR, 3.52; 95% CI, 3.39 to 3.66) and substance use disorders (7.0% vs. 2.3%; AOR, 3.82; 95% CI, 3.66 to 3.99). When anxiety and other disorders were included, the rate of mental illness was 39.3% in the top 1% compared to 21.3% (AOR, 2.39; 95% CI, 2.34 to 2.45).
  
  
  
  A high burden of mental illness and addiction among HCUs warrants its consideration in the design and delivery of services targeting HCUs.
authors.affiliation: Department of Psychiatry, Women's College Hospital, Toronto, Ontario Department of Psychiatry, University of Toronto, Toronto, Ontario Women's College Research Institute, Toronto, Ontario jennifer.hensel@mail.utoronto.ca.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Hensel
authors.affiliation: Department of Psychiatry, Women's College Hospital, Toronto, Ontario Department of Psychiatry, University of Toronto, Toronto, Ontario Women's College Research Institute, Toronto, Ontario.
authors.forename: Valerie H
authors.initials: VH
authors.lastname: Taylor
authors.affiliation: Women's College Research Institute, Toronto, Ontario Institute for Clinical Evaluative Sciences, Toronto, Ontario.
authors.forename: Kinwah
authors.initials: K
authors.lastname: Fung
authors.affiliation: Department of Psychiatry, Women's College Hospital, Toronto, Ontario Department of Psychiatry, University of Toronto, Toronto, Ontario Women's College Research Institute, Toronto, Ontario Institute for Clinical Evaluative Sciences, Toronto, Ontario.
authors.forename: Simone N
authors.initials: SN
authors.lastname: Vigod
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D017048:Health Care Costs / Q000706:statistics & numerical data*; D006296:Health Services / Q000191:economics / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000191:economics / Q000453:epidemiology / Q000628:therapy; D008875:Middle Aged; D009313:National Health Programs / Q000706:statistics & numerical data; D009864:Ontario; D019966:Substance-Related Disorders / Q000191:economics / Q000453:epidemiology / Q000628:therapy
keywords: co-morbidity; health services; high-cost users