Interaction between mental health conditions and hip fracture on the 30-day risk of infection among older adults: a Danish matched cohort study.

purposeInfections are a frequent complication following hip fracture (HF) surgery. Although approximately 30% of patients undergoing HF surgery have a mental health condition, its potential interaction on the risk of post-operative infection remains uncertain.

methodsUsing Danish nationwide registries, we included a cohort of patients with HF aged ≥ 65 years operated during 2004-21 (n=100 335) and an age- and sex-matched comparison cohort from the general population without HF at the index date (n=498 943). Mental health conditions were identified using diagnosis codes F00-F48. Outcomes were hospital-treated infections (H-TIs) and hospital- or community-treated infections (HC-TIs) within 30 days after surgery. Cumulative incidence with 95% confidence intervals (CI) was estimated with death as competing risk. Interaction was assessed on an absolute and relative scale.

resultsThe highest incidence of H-TIs was observed among patients with HF and mood disorders (18.1%, 95% CI: 17.3-19.0) and comparators with anxiety disorders (2%, 95% CI: 1.8-2.5). Among patients with HF, the highest incidence of HC-TIs was in those with dementia (43.0%, 95% CI: 42.2-43.9). Likewise, comparators with dementia had the highest incidence of HC-TIs (18.4%, 95% CI: 17.9-18.8). Across mental health condition categories, attributable fractions ranged from 1.1% to 32.3% for H-TIs and 10.8%-19.7% for HC-TIs. The strongest synergistic effect was observed in patients with psychoactive substance use for both H-TIs and HC-TIs.

conclusionsPatients with HF and mental health conditions are at higher risk of infection than comparators. Mental health conditions and HF interact synergistically, which increases the infection risk by more than 30%, highlighting the need for targeted treatment for patients with HF and mental health conditions.