Depression and Risk of Delirium in Older Adults: A Retrospective Cohort Study Using German Primary Care Data

Background: Depression and delirium are common neuropsychiatric disorders in older adults. Although studies suggest an association between the two conditions, evidence regarding the long-term risk of delirium in older patients with depression in outpatient primary care remains limited. Objective: This study examined the relationship between depression and delirium in individuals aged ≥65 years. Methods: This retrospective cohort study used data from the German IQVIA Disease Analyzer database. It included individuals aged ≥65 years who received their first diagnosis of depression between 2005 and 2023. Using propensity score matching, patients with depression were matched 1:1 with individuals without depression. The primary outcome was incident delirium (ICD-10: F05). Time-dependent Cox regression models were applied for up to ten years of follow-up. Results: After matching, the study population consisted of 203,888 individuals (mean age: 75.8 years; 66% female). The incidence of delirium was higher in patients with depression than in controls (2.0% vs. 1.3%). Depression was associated with an elevated risk of delirium within the first two years after diagnosis (HR 1.42; 95% CI 1.14-1.75) and between six and ten years (HR 1.48; 95% CI 1.05-2.11). No statistically significant association was observed between years 3 and 5. Incident dementia was also associated with delirium (HR 1.52; 95% CI 1.14-2.02). Conclusions: Among older adults receiving outpatient care, depression was associated with a higher rate of subsequently documented delirium. These results complement existing evidence from inpatient settings. Due to the observational nature of the study, causal inferences cannot be made. In a sensitivity analysis excluding individuals with dementia at baseline, the association remained statistically significant across all intervals (HR 1.74, 1.53, and 1.82 for 0-2, 3-5, and 6-10 years, respectively).