Delirium superimposed on dementia in a community-dwelling managed care population: a 3-year retrospective study of occurrence, costs, and utilization.

BACKGROUND Dementia is a growing public health problem and a well-described risk factor for delirium. Yet little is known about delirium superimposed on dementia in community-dwelling populations. The purpose of this study was to examine the 3-year occurrence, healthcare utilization, and costs associated with delirium superimposed on dementia in community-dwelling persons. METHODS We used a 3-year cross-sectional, retrospective design with an administrative database from a large managed care organization. Four individually matched samples of 699 individuals each were selected for comparison purposes: delirium superimposed on dementia (DSD), dementia alone, delirium alone, and a control group with neither delirium nor dementia. The occurrence rate of DSD was calculated by measuring those individuals with a dementia diagnosis that were also coded with an International Classification of Diseases, Ninth Edition Clinical Modification (ICD-9 CM) code for delirium or delirium with dementia. RESULTS Of the total sample of 76,688 persons aged 65 years or older in the managed care organization, 7347 (10%) were coded as having dementia, and an additional 763 (1%) as having delirium alone. Among the 7347 with dementia, 976 (13%) had DSD, representing 1.3% of the total sample. After log transformation of total costs and adjustment for multiple covariates, the adjusted mean total health care costs remained significantly higher for the DSD group than for all other groups. CONCLUSIONS This study is the first to report the occurrence rate of DSD in a community-dwelling population, and to demonstrate the substantial health care costs and utilization associated with DSD.