title: Prevalence, determinants and patterns of multimorbidity in primary care: a systematic review of observational studies.
abstract: BACKGROUND
  Multimorbidity is a major concern in primary care. Nevertheless, evidence of prevalence and patterns of multimorbidity, and their determinants, are scarce. The aim of this study is to systematically review studies of the prevalence, patterns and determinants of multimorbidity in primary care.
  
  
  METHODS
  Systematic review of literature published between 1961 and 2013 and indexed in Ovid (CINAHL, PsychINFO, Medline and Embase) and Web of Knowledge. Studies were selected according to eligibility criteria of addressing prevalence, determinants, and patterns of multimorbidity and using a pretested proforma in primary care. The quality and risk of bias were assessed using STROBE criteria. Two researchers assessed the eligibility of studies for inclusion (Kappa= 0.86).
  
  
  RESULTS
  We identified 39 eligible publications describing studies that included a total of 70,057,611 patients in 12 countries. The number of health conditions analysed per study ranged from 5 to 335, with multimorbidity prevalence ranging from 12.9% to 95.1%. All studies observed a significant positive association between multimorbidity and age (odds ratio [OR], 1.26 to 227.46), and lower socioeconomic status (OR, 1.20 to 1.91). Positive associations with female gender and mental disorders were also observed. The most frequent patterns of multimorbidity included osteoarthritis together with cardiovascular and/or metabolic conditions.
  
  
  CONCLUSIONS
  Well-established determinants of multimorbidity include age, lower socioeconomic status and gender. The most prevalent conditions shape the patterns of multimorbidity. However, the limitations of the current evidence base means that further and better designed studies are needed to inform policy, research and clinical practice, with the goal of improving health-related quality of life for patients with multimorbidity. Standardization of the definition and assessment of multimorbidity is essential in order to better understand this phenomenon, and is a necessary immediate step.
authors.affiliation: Central Research Unit, Institut Universitari d'Investigació en Atenció Primària Jordi Gol, Barcelona, Catalunya, Spain; Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), Spain.
authors.forename: Concepció
authors.initials: C
authors.lastname: Violan
authors.affiliation: Central Research Unit, Institut Universitari d'Investigació en Atenció Primària Jordi Gol, Barcelona, Catalunya, Spain; Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), Spain.
authors.forename: Quintí
authors.initials: Q
authors.lastname: Foguet-Boreu
authors.affiliation: Central Research Unit, Institut Universitari d'Investigació en Atenció Primària Jordi Gol, Barcelona, Catalunya, Spain; Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), Spain.
authors.forename: Gemma
authors.initials: G
authors.lastname: Flores-Mateo
authors.affiliation: Centre of Academic Primary Care, School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors.forename: Chris
authors.initials: C
authors.lastname: Salisbury
authors.affiliation: Department of Public Health and Primary Care, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Jeanet
authors.initials: J
authors.lastname: Blom
authors.affiliation: Institute of General Practice and Family Medicine, Jena University Hospital, Friedrich-Schiller-University, School of Medicine, Jena, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Freitag
authors.affiliation: Discipline of General Practice, National University of Ireland, Galway, Ireland.
authors.forename: Liam
authors.initials: L
authors.lastname: Glynn
authors.affiliation: Institute of General Practice, Johann Wolfgang Goethe University, Frankfurt/Main, Frankfurt, Germany.
authors.forename: Christiane
authors.initials: C
authors.lastname: Muth
authors.affiliation: Health Services & Policy Research Group, School of Medicine, University of Exeter, Exeter, United Kingdom.
authors.forename: Jose M
authors.initials: JM
authors.lastname: Valderas
mesh_terms: D000367:Age Factors; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D011320:Primary Health Care / Q000379:methods; D011788:Quality of Life; D012737:Sex Factors; D012959:Socioeconomic Factors; D064887:Observational Studies as Topic