title: The synergistic effect of functional status and comorbidity burden on mortality: a 16-year survival analysis.
abstract: OBJECTIVE
  The relationship between disability and comorbidity on mortality is widely perceived as additive in clinical models of frailty.
  
  
  METHODS
  National data were retrospectively extracted from medical records of community hospital.
  
  
  METHODS
  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.
  
  
  METHODS
  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.
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, National University Health System, Singapore, Singapore.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Chen
authors.affiliation: College of Public Health and Health Professions, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Isaac
authors.initials: I
authors.lastname: Sia
authors.affiliation: Departments of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong SAR, China.
authors.forename: Hon-ming
authors.initials: HM
authors.lastname: Ma
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, National University Health System, Singapore, Singapore.
authors.forename: Bee Choo
authors.initials: BC
authors.lastname: Tai
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, National University Health System, Singapore, Singapore.
authors.forename: Angela
authors.initials: A
authors.lastname: Cheong
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, National University Health System, Singapore, Singapore.
authors.forename: Ngan Phoon
authors.initials: NP
authors.lastname: Fong
authors.affiliation: Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, Singapore, Singapore.
authors.forename: Shi Yu Julia
authors.initials: SY
authors.lastname: Tan
authors.affiliation: Medical Services, Ang Mo Kio Thye Hua Kwan Hospital, Singapore, Singapore.
authors.forename: Kin Ming
authors.initials: KM
authors.lastname: Chan
authors.affiliation: Medical Services, St Luke's Hospital, Singapore, Singapore.
authors.forename: Boon Yeow
authors.initials: BY
authors.lastname: Tan
authors.affiliation: Medical Services, St Andrew's Community Hospital, Singapore, Singapore.
authors.forename: Edward
authors.initials: E
authors.lastname: Menon
authors.affiliation: Bright Vision Hospital, Singapore, Singapore.
authors.forename: Chye Hua
authors.initials: CH
authors.lastname: Ee
authors.affiliation: Bright Vision Hospital, Singapore, Singapore.
authors.forename: Kok Keng
authors.initials: KK
authors.lastname: Lee
authors.affiliation: Department of Rehabilitation Medicine, Singapore General Hospital, Singapore, Singapore.
authors.forename: Yee Sien
authors.initials: YS
authors.lastname: Ng
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, National University Health System, Singapore, Singapore; Genome Institute of Singapore, Agency for Science, Technology, and Research, Singapore, Singapore; Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore, Singapore; Department of Statistics and Applied Probability, National University of Singapore, Singapore, Singapore.
authors.forename: Yik Ying
authors.initials: YY
authors.lastname: Teo
authors.affiliation: Ministry of Health, Singapore, Singapore.
authors.forename: Stefan
authors.initials: S
authors.lastname: Ma
authors.affiliation: Ministry of Health, Singapore, Singapore.
authors.forename: Derrick
authors.initials: D
authors.lastname: Heng
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, National University Health System, Singapore, Singapore; Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, Singapore, Singapore.
authors.forename: Gerald Choon-Huat
authors.initials: GC
authors.lastname: Koh
mesh_terms: D015897:Comorbidity; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007297:Inpatients; D008297:Male; D008954:Models, Biological; D012189:Retrospective Studies; D012307:Risk Factors; D012846:Singapore / Q000453:epidemiology; D012959:Socioeconomic Factors; D016019:Survival Analysis