Thirty-day prevalence of delirium among very old people: a population-based study of very old people living at home and in institutions.

Delirium has mainly been studied in various patient samples and in people living in institutions. The present study investigates the 30-day prevalence of delirium in a population-based sample of very old people in northern Sweden and Finland. Seven hundred and eight persons aged 85 years and older from the GErontological Regional DAtabase (GERDA) were assessed. Information was also collected from relatives, carers and medical records. Assessments performed were among others the Organic Brain Syndrome (OBS) scale, the Mini Mental State Examination (MMSE), and the Geriatric Depression Scale-15 (GDS-15). Delirium, depression and dementia diagnoses were based on the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) criteria. The prevalence of delirium was 17% among 85 year-olds, 21% among 90 year-olds and 39% among participants aged 95 years and older (p<0.001). Delirium prevalence among individuals without dementia was lower than among those with dementia (5% vs. 52%, p<0.001). Factors independently associated with delirium superimposed on dementia in a multivariate logistic regression model were depression (Odds Ratio (OR)=2.0, 95% Confidence Interval (CI)=1.2-3.3), heart failure (OR=2.1, 95% CI=1.2-3.7), institutional living (OR 4.4, 95% CI=2.4-8.2) and prescribed antipsychotics (OR=3.0, 95% CI=1.5-6.0). Delirium is highly prevalent among very old people with dementia. Depression, heart failure, institutional living and prescribed antipsychotic medication seem to be associated with delirium.