Population-based repeated cross-sectional study of hospitalizations for comorbid physical and psychiatric disorders in young adults in Ontario, Canada

Purpose — To measure trends in the rates and costs of hospitalizations over a 15-year period among young adults with physical and/or psychiatric disorders.

Methods — This population-based, repeated cross-sectional study identified all 18- to 26- year-olds hospitalized in Ontario, Canada from April 1, 2003 and March 31, 2018 (fiscal years 2003–2017). Using discharge diagnoses, we assigned hospitalizations to one of four categories: 1) psychiatric disorder only; 2) primary psychiatric disorder with comorbid physical illness; 3) primary physical with comorbid psychiatric disorder; and 4) physical illness only. We compared health service utilization and changes in rates of hospitalizations over time using restricted cubic spline regression. Secondary outcome measures included change in hospital costs for each hospitalization category over the study period.

Results — Of 1,076,951 hospitalizations in young adults (73.7% female), 195,726 (18.2%) had a psychiatric disorder (either primary or comorbid). There were 129,676 hospitalizations (12.0%) with psychiatric disorders only, 36,287 (3.4%) with primary psychiatric and comorbid physical disorders, 29,763 (2.8%) with primary physical and comorbid psychiatric disorders, and 881,225 (81.8%) with physical disorders only. Rates of hospitalization for psychiatric disorders only increased 81% from 4.32 to 7.84/1,000 population, and those with physical health disorders with comorbid psychiatric disorders increased 172% from 0.47 to 1.28/1,000 population. Substance-related disorders were the most common comorbid psychiatric disorders among youth hospitalized for physical illness and increased 260% from 0.9 to 3.3/1,000 population.

Discussion — Hospitalizations among young adults with primary and comorbid psychiatric disorders have increased significantly over the past 15 years. Health system resources should be adequately directed to meet the shifting and complex needs of hospitalized young adults.