We found that delirium was very uncommon (< 0.5%) in this population of older Canadians without dementia living in their usual place of residence. Delirium had a notably poor outcome, with a 5-year survival comparable with advanced dementia.
Our findings must be interpreted with caution. Although the CSHA sample was large, the number of individuals diagnosed with delirium (21) was small, resulting in wide confidence intervals. The small number of cases and resulting wide confidence intervals serve to illustrate an important point, which is that delirium is very uncommon outside acute care settings.
Delirium is often superimposed on dementia. A recent study of community-dwelling older adults in a managed care organization administrative database in the United States found that 13% of older adults with dementia had superimposed delirium [14]. In focusing solely on delirium diagnosed in the absence of underlying dementia, our study probably underestimates the true prevalence of delirium in community-dwelling older adults. This is especially true given that the prevalence of dementia in residents of Long Term Care in this CSHA sample is high (64%) and that only delirium cases occurring among the remaining 36% would have been included in our study. The direction of bias in our study, in which cases of delirium superimposed on dementia were not counted as delirium, probably resulted in a more conservative comparison of outcomes, given that individuals with dementia underlying their delirium might reasonably be expected to have poorer outcomes than individuals who were previously cognitively intact. Including these individuals in the delirium group might therefore have led to a finding of even poorer outcomes in comparisons of delirium with dementia of graded severity.
As in other studies, the diagnosis of both delirium and dementia was clinical, although the use of multiple observers and preliminary and final diagnostic opinions at a case conference are important aids to judgment. In particular, diagnosis of dementia relied on comprehensive clinical and neuropsychological assessments and not on a history of previously diagnosed dementia.
The finding that cognitive function, as measured by the 3MS, was better than that seen in moderate and severe dementia, yet survival was not, provides valuable new information. The prevalence of urinary incontinence among individuals with delirium was higher than that observed in all cognitive subgroups except severe dementia. This may reflect the association of delirium with underlying frailty and medical comorbidity [2]. In contrast, individuals with delirium (but no underlying dementia) had duration of functional (dressing) impairment similar to those with NCI, CIND and mild-moderate dementia, but shorter than those with severe dementia, probably as a consequence of their better pre-morbid cognitive function.
Delirium is known to be common and associated with acute illness in older patients presenting to and admitted to acute care facilities [1–5]. One might expect delirium in older adults outside of acute care to be associated with high mortality in the short term owing to underlying acute illness that is not being treated. While 5-year mortality in the 21 patients identified in this study was high, several individuals survived hundreds of days following their diagnosis, so their 5-year mortality was not driven by deaths immediately following the study assessment. This suggests that while delirium operates as a marker of frailty (and thus increases susceptibility), overall lethality commonly depends also on an accumulated burden of deficits [11].
Few studies have investigated delirium outside of acute care. One study found that 10% of a sample of 199 older adults without dementia aged 85+ who were community-dwelling and free of dementia and delirium at baseline developed an episode of delirium over a 3 year follow-up period, and that these individuals had higher mortality than those who had not developed delirium [8]. Our results are consistent in that we found increased 5-year mortality in those diagnosed with delirium, though we employed a point-prevalence design rather than studying incidence of delirium. The 1981 community-based Eastern Baltimore Mental Health Survey clinically diagnosed delirium in 6 of 810 adults; the prevalence was 1.1% in adults over age 55 and 13.6% in the > = 85 age group [7]. We found a much lower prevalence of delirium (<0.5%) even among subjects aged 85 and over. Caution must be employed in considering this comparison in view of the small numbers of cases in both studies: the 13.6% prevalence was based on a single case of delirium in a sub-sample of 16 individuals aged 85 and over [7]. Although our prevalence estimate is also based on a small number of cases, our denominator is much larger. A Swedish prevalence study involving older adults in various care settings found a high prevalence of delirium: 58% in nursing homes, 35% in old people's homes and 35% in older people living in their own homes with home care services [9]. The prevalence in our study population of adults aged ≥ 65 years was much lower. One possible explanation is that our study was population-based, whereas in the Swedish study the prevalence of dementia was high and all the older adults included were receiving care services and thus represented a population that was more frail (and at higher risk of delirium) than ours. In the CSHA, clinical diagnoses of delirium and dementia were mutually exclusive. Given that cognitive impairment and dementia are established risk factors for delirium [8, 15], one would expect lower prevalence of delirium in non-demented older adults.
