title: The increasing burden and complexity of multimorbidity.
abstract: BACKGROUND
  Multimorbidity, the co-occurrence of two or more chronic conditions, is common among older adults and is known to be associated with high costs and gaps in quality of care. Population-based estimates of multimorbidity are not readily available, which makes future planning a challenge. We aimed to estimate the population-based prevalence and trends of multimorbidity in Ontario, Canada and to examine patterns in the co-occurrence of chronic conditions.
  
  
  METHODS
  This retrospective cohort study includes all Ontarians (aged 0 to 105 years) with at least one of 16 common chronic conditions. Descriptive statistics were used to examine and compare the prevalence of multimorbidity by age and number of conditions in 2003 and 2009. The co-occurrence of chronic conditions among individuals with multimorbidity was also explored.
  
  
  RESULTS
  The prevalence of multimorbidity among Ontarians rose from 17.4% in 2003 to 24.3% in 2009, a 40% increase. This increase over time was evident across all age groups. Within individual chronic conditions, multimorbidity rates ranged from 44% to 99%. Remarkably, there were no dominant patterns of co-occurring conditions.
  
  
  CONCLUSIONS
  The high prevalence of multimorbidity and numerous combinations of conditions suggests that single, disease-oriented management programs may be less effective or efficient tools for high quality care compared to person-centered approaches.
authors.affiliation: Cancer Screening, Cancer Care Ontario/Action Cancer Ontario, 505 University Avenue, Room 18-14, Toronto, M5G 1X3, Ontario, Canada. Anna.Kone@cancercare.on.ca.|Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, ON, Canada. Anna.Kone@cancercare.on.ca.|Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada. Anna.Kone@cancercare.on.ca.
authors.forename: Anna J Koné
authors.initials: AJ
authors.lastname: Pefoyo
authors.affiliation: Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, ON, Canada. susan.bronskill@ices.on.ca.|Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. susan.bronskill@ices.on.ca.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Bronskill
authors.affiliation: Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, ON, Canada. gruneir@ualberta.ca.|Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. gruneir@ualberta.ca.|Women's College Research Institute, Women's College Hospital, Toronto, ON, Canada. gruneir@ualberta.ca.|Department of Family Medicine, University of Alberta, Edmonton, AB, Canada. gruneir@ualberta.ca.
authors.forename: Andrea
authors.initials: A
authors.lastname: Gruneir
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. andrew.calzavara@ices.on.ca.
authors.forename: Andrew
authors.initials: A
authors.lastname: Calzavara
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. kthavorn@ohri.ca.|Ottawa Hospital Research Institute, The Ottawa Hospital, Ottawa, ON, Canada. kthavorn@ohri.ca.|School of Epidemiology, Public Health and Preventive Medicine, University of Ottawa, Ottawa, ON, Canada. kthavorn@ohri.ca.
authors.forename: Kednapa
authors.initials: K
authors.lastname: Thavorn
authors.affiliation: Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, ON, Canada. yelena.petrosyan@mail.utoronto.ca.
authors.forename: Yelena
authors.initials: Y
authors.lastname: Petrosyan
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. colleen.maxwell@uwaterloo.ca.|Schools of Pharmacy and Public Health and Health Systems, University of Waterloo, Waterloo, ON, Canada. colleen.maxwell@uwaterloo.ca.
authors.forename: Colleen J
authors.initials: CJ
authors.lastname: Maxwell
authors.affiliation: Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, ON, Canada. yuqing.bai@utoronto.ca.|Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. yuqing.bai@utoronto.ca.
authors.forename: YuQing
authors.initials: Y
authors.lastname: Bai
authors.affiliation: Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, ON, Canada. walter.wodchis@utoronto.ca.|Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. walter.wodchis@utoronto.ca.|Toronto Rehabilitation Institute, Toronto, ON, Canada. walter.wodchis@utoronto.ca.
authors.forename: Walter P
authors.initials: WP
authors.lastname: Wodchis
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D002908:Chronic Disease / Q000453:epidemiology*; D015897:Comorbidity; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D015995:Prevalence; D012189:Retrospective Studies; D012959:Socioeconomic Factors; D055815:Young Adult