Combined impacts of multimorbidity and mental disorders on frequent emergency department visits: a retrospective cohort study in Quebec, Canada

Abstract

Background: Multimorbidity and mental disorders are independently associated with frequent visits to the emergency department (≥ 3 visits/yr), but their interaction has been little studied. We aimed to measure the interaction between mental disorders and physical multimorbidity with respect to frequent visits to the emergency department.

Methods: We conducted a population-based cohort study of adults in Quebec from 2012 to 2016, using the Quebec Integrated Chronic Disease Surveillance System. We assessed multimorbidity as the number of physical illnesses and mental disorders as serious (psychotic or bipolar disorders), common or absent, using data from 2012 to 2014. We counted emergency department visits from 2014 to 2015. We used logistic regression to estimate interaction on frequent visits to the emergency department from 2 perspectives: of public health (additive scale as differences in risk) and of individual patients (multiplicative scale as odds ratios).

Results: Each additional physical illness was associated with a greater increase in the absolute risk of frequent visits to the emergency department for people with mental disorders. Between 0 and ≥ 4 physical conditions, the absolute risk increased more for individuals with serious mental disorders (16.2%) than common (15.3%) or no disorders (11.4%). On the relative scale, for people with no mental disorders and ≥ 4 physical conditions, odds of frequent visits to the emergency department were 6.2 (95% confidence interval [CI] 6.08-6.35) times the odds for people with no physical conditions. For individuals with common and serious mental illnesses, corresponding odds ratios were 4.75 (95% CI 4.60-4.90) and 3.7 (95% CI 3.18-3.57), respectively.

Interpretation: Mental disorders interact with physical multimorbidity to increase the odds of frequent visits to the emergency department. More research is needed on interventions that promote high-quality care for mental illness, especially in the context of physical multimorbidity.

Figure 1:

Public health impact (absolute scale). Adjusted* proportions of frequent users of the emergency department (ED) (≥ 3 admissions/yr) by number of physical conditions in Quebec, stratified by mental disorder status, fiscal year 2014/15. (A) Adjusted proportions (95% confidence interval [CI]) of frequent ED users with common mental disorders (n = 598 276), versus no mental disorder (n = 4 638 633). (B) Adjusted proportions (95% CI) of frequent ED users with serious mental disorders (n = 79 923), versus no mental disorder (n = 4 638 633). *Proportions adjusted for age, sex, material deprivation, social deprivation and rurality. The solid, lowermost line represents the base proportion admitted with neither mental nor physical illnesses. The bottom, dotted curve represents proportions of frequent ED users with no mental disorder. The middle, dotted and dashed curve represents the expected proportion estimated from simple addition of effects of physical multimorbidity and mental disorders. The topmost, dashed curve corresponds to the actual observed proportions. The light teal area corresponds to frequent admissions from mental disorders, and the dark teal area corresponds to the excess ED admissions owing to synergy.