Relative risk and risk factors of all-cause, natural-cause and external-cause mortality after psychiatric hospitalisation: a population-based electronic health-record study in Hong Kong.

BACKGROUND

Discharge from psychiatric hospitalisation is associated with increased mortality risk, but risk estimates across fine-grained post-discharge intervals and identified risk factors are lacking.

METHODS

We conducted a population-based study utilising a medical health record database of public healthcare services in Hong Kong. We identified all individuals aged ≥12 years who had been discharged from psychiatric inpatient units between January-01-2006 and December-31-2021. Individuals without history of psychiatric hospitalisation attending primary care clinics during the same period served as comparison group (i.e., primary-care clinics [PCC] cohort). Survival analyses estimated cumulative incidences and hazard ratios (HRs) for all-cause, natural-cause and external-cause mortality across discrete intervals from ≤1 month to >10 years post-discharge. Risk factors for excess mortality 1-year and 10-year post-discharge were evaluated.

FINDINGS: The discharged cohort comprised 114,395 patients with 975,229 controls. Within the first-year post-discharge, within the deceased patient group, natural causes and suicide-related mortality accounted for 65.8% and 18.8% of deaths in the discharged cohort, and for 87.8% and 1.6% of deaths in the PCC cohort. The relative proportion of all deaths due to suicide in the discharged cohort decreased from 18.8% at 1-year to 11.7% at 10-year, while the relative proportion of all deaths from natural causes increased from 65.8% at 1-year to 73.3% at 10-year. Respiratory diseases (year 1 = 30.6%, year 10 = 35.0%) and cardiovascular diseases (year 1 = 10.7%, year 10 = 11.0%) were consistently leading causes of natural deaths. Relative all-cause mortality risk peaked within 1-month post-discharge (HR = 10.31 [95% confidence interval (CI) = 9.36-11.36]), remaining high at 1-year (HR = 3.40 [95% CI = 3.17-3.65]) and 10-year (HR = 2.61 [95% CI = 2.52-2.69]). External-cause mortality, particularly suicide-related mortality, showed extremely high risk during 1-month (HR = 78.54 [95% CI = 52.64-117.18]), and remained high at 1-year (HR = 42.40 [95% CI = 30.02-59.87]) and 10-year (HR = 10.29 [95% CI = 8.75-12.10]). Depression diagnosis at discharge conferred the highest short-term suicide risk, while substance/alcohol use disorders showed the highest long-term any-cause mortality risk. Risk factors for premature mortality within 1-year and 10-year post-discharge included male sex, old age, not receiving social/disability allowance, greater physical morbidity burden, self-harm history, and poor discharge psychiatric status. Ethnicity data were not available in the database.

INTERPRETATION: The immediate post-discharge phase is a critical window for targeted and diagnosis-specific intervention, including psychiatric/social/financial support. Future research should prioritise the development of robust risk prediction models that incorporate key risk factors identified to facilitate personalised care and improves post-discharge outcomes for high-risk individuals.

FUNDING: Health and Medical Research Fund.