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Subsyndromal Delirium in Older Long-Term Care Residents: Incidence, Risk Factors, and Outcomes


Address correspondence to Dr. Martin G. Cole, Department of Psychiatry, St. Mary's Hospital Center, 3830 Avenue Lacombe, Montreal, Quebec H3T 1M5, Canada. E-mail:



To determine the incidence of, risk factors for, and outcomes of subsyndromal delirium (SSD) in older long-term care (LTC) residents and, secondarily, to explore the use of a more-restrictive definition of SSD.


Cohort study with repeated weekly assessments for up to 6 months.


Seven LTC facilities in Montreal and Quebec City, Canada.


One hundred four LTC residents aged 65 and older and free of delirium core symptoms at baseline.


The Mini-Mental State Examination (MMSE), Confusion Assessment Method (CAM), Delirium Index (DI), Hierarchic Dementia Scale (HDS), and Barthel Index (BI) were completed at baseline. The MMSE, CAM, and DI were repeated weekly for 6 months. SSD1 required one or more CAM core symptoms; SSD2, a more-restrictive definition, required two or more CAM core symptoms. Outcomes at 6 months were decline on the MMSE, HDS, and BI; mortality; and a composite outcome.


Sixty-eight of 104 residents had SSD1. In survival analysis, the incidence was 5.2 (95% confidence interval (CI) = 4.1–6.7) per 100 person-weeks of follow-up. In multivariate analysis, risk factors were male sex and more-severe cognitive impairment at baseline. The differences in outcomes between residents with and without SSD1 were small and not statistically significant. SSD2 had a lower incidence (1.3, 95% CI = 0.9–1.9), similar risk factors, and statistically significantly worse cognitive outcomes.


SSD2 appears to be a clinically important disorder in older LTC residents. Despite limited statistical power, these findings have potentially important implications for clinical practice and research in LTC settings.

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