The synergistic effect of functional status and comorbidity burden on mortality: a 16-year survival analysis

PLoS One. 2014 Aug 29;9(8):e106248. doi: 10.1371/journal.pone.0106248. eCollection 2014.

Abstract

Objectives: The relationship between disability and comorbidity on mortality is widely perceived as additive in clinical models of frailty.

Design: National data were retrospectively extracted from medical records of community hospital.

Data sources: There were of 12,804 acutely-disabled patients admitted for inpatient rehabilitation in Singapore rehabilitation community hospitals from 1996 through 2005 were followed up for death till 31 December 2011.

Outcome measure: Cox proportional-hazards regression to assess the interaction of comorbidity and disability at discharge on all-cause mortality.

Results: During a median follow-up of 10.9 years, there were 8,565 deaths (66.9%). The mean age was 73.0 (standard deviation: 11.5) years. Independent risk factors of mortality were higher comorbidity (p<0.001), severity of disability at discharge (p<0.001), being widowed (adjusted hazard ratio [aHR]: 1.38, 95% confidence interval [CI]:1.25-1.53), low socioeconomic status (aHR:1.40, 95%CI:1.29-1.53), discharge to nursing home (aHR:1.14, 95%CI:1.05-1.22) and re-admission into acute care (aHR:1.54, 95%CI:1.45-1.65). In the main effects model, those with high comorbidity had an aHR = 2.41 (95%CI:2.13-2.72) whereas those with total disability had an aHR = 2.28 (95%CI:2.12-2.46). In the interaction model, synergistic interaction existed between comorbidity and disability (p<0.001) where those with high comorbidity and total disability had much higher aHR = 6.57 (95%CI:5.15-8.37).

Conclusions: Patients with greater comorbidity and disability at discharge, discharge to nursing home or re-admission into acute care, lower socioeconomic status and being widowed had higher mortality risk. Our results identified predictive variables of mortality that map well onto the frailty cascade model. Increasing comorbidity and disability interacted synergistically to increase mortality risk.

Publication types

  • Clinical Trial
  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Comorbidity*
  • Female
  • Follow-Up Studies
  • Humans
  • Inpatients
  • Male
  • Models, Biological*
  • Retrospective Studies
  • Risk Factors
  • Singapore / epidemiology
  • Socioeconomic Factors
  • Survival Analysis*

Grants and funding

This study was supported by a National University of Singapore (NUS) Start-Up Grant, the NUS Provost Matching Grant, the NUS Academic Research Fund, Ministry of Health (Singapore) Health Services Research Competitive Research Grant Number HSRG/0006/2013, Singapore National Medical Research Council Research Fellowship and Schulich Graduate Scholarship, University of Western Ontario. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.