Characteristics of patients with mental illness and persistent high-cost status: a population-based analysis

BACKGROUND: Most of the literature on high-cost users of health care has evaluated this population as a whole, but few studies have focused on high-cost patients with mental illness and whether they persist in the high-cost state. We sought to analyze this patient population in depth and determine predictors of persistency in the high-cost state. METHODS: We used 8 years of longitudinal patient-level population data (2010-2017) from Ontario to follow high-cost patients (those in and above the 90th percentile of the cost distribution) with mental illness. We classified high-cost status, based on the proportion of the study period that patients spent in the high-cost state, as persistent (6-8 yr), sporadic (1-2 yr) or moderate (3-5 yr). We compared characteristics between groups and determined predictors of being a patient with mental illness and persistent high-cost status. RESULTS: Among 52 638 patients with mental illness and high-cost status, 18 149 (34.5%) were considered persistent high cost. These patients had higher mean annual costs of care ($44 714, 95% confidence interval [CI] $43 724-$45 703) than patients with sporadic ($23 205, 95% CI $22 741-$23 668) and moderate ($31 055, 95% CI $30 359-31 751) status, largely owing to psychiatric hospital admissions. Patients with mental illness and persistent high-cost status were more likely to be female, older, long-term residents of Ontario (information ascertained from the Immigrants, Refugees and Citizenship Canada Database), living in low-income or urban areas, or to have comorbidities. The strongest predictors of persistent (v. sporadic) high-cost status were HIV (relative risk ratio [RRR] 4.32, 95% CI 3.08-6.06), psychosis (RRR 3.41, 95% CI 3.25-3.58) and dementia (RRR 3.21, 95% CI 2.81-3.68). INTERPRETATION: Among patients with mental illness and high-cost status, persistence in the high-cost state was determined mainly by psychosis and other comorbidities. Quality-of-care interventions directed at managing psychosis and multimorbidity, as well as preventive interventions to target patients with mental illness before they enter the persistent high-cost state, are needed.