Population-based incidence rate of in-hospital delirium in older adults in Norway-a HUNT study.

BACKGROUND

Most studies of delirium occurrence are based on selected hospitalised populations or administrative data. We aimed to estimate the incidence rate of in-hospital delirium in older adults and to assess use of the International Classification of Diseases, 10th Revision (ICD-10) delirium code (F05) in electronic health records.

METHODS

This population-based cohort study included 9956 participants aged ≥70 years from HUNT4 70+. Participants were followed from the date of study participation (2017-19) until 31 December 2023. In-hospital delirium was identified by retrospective chart review of all admissions during follow-up, using Diagnostic and Statistical Manual of Mental Disorders, fifth edition criteria. Incidence rates were estimated using the first delirium episode per participant, weighted for non-participation.

RESULTS

During follow-up, 1507 participants (15.1%) experienced ≥1 in-hospital delirium episode. The weighted incidence rate was 33.1 (95% CI 31.5-34.9) per 1000 person-years and increased with age from 11.4 (age 70-74) to 109.0 (age ≥90) per 1000 person-years. Men had higher incidence rates than women across age groups. Among admissions with delirium, 11.9% had an ICD-10 discharge delirium diagnosis code (F05).

CONCLUSION

In-hospital delirium was common, increased markedly with age and was rarely captured by diagnostic coding. Low coding rates suggest that routine health-care data substantially underestimate delirium burden. Under-recognition of delirium may limit opportunities for follow-up in a group at high risk of adverse outcomes. With an ageing population, the burden of delirium is likely to increase for individuals and health-care systems. Our findings support systematic approaches to improve identification and management.