title: In rheumatoid arthritis, country of residence has an important influence on fatigue: results from the multinational COMORA study.
abstract: OBJECTIVE
  To investigate the relationship between country of residence and fatigue in RA, and to explore which country characteristics are related to fatigue.
  
  
  METHODS
  Data from the multinational COMORA study were analysed. Contribution of country of residence to level of fatigue [0-10 on visual analogue scale (VAS)] and presence of severe fatigue (VAS ⩾ 5) was explored in multivariable linear or logistic regression models including first socio-demographics and objective disease outcomes (M1), and then also subjective outcomes (M2). Next, country of residence was replaced by country characteristics: gross domestic product (GDP), human development index (HDI), latitude (as indicator of climate), language and income inequality index (gini-index). Model fit (R(2)) for linear models was compared.
  
  
  RESULTS
  A total of 3920 patients from 17 countries were included, mean age 56 years (s.d. 13), 82% females. Mean fatigue across countries ranged from 1.86 (s.d. 2.46) to 4.99 (s.d. 2.64) and proportion of severe fatigue from 14% (Venezuela) to 65% (Egypt). Objective disease outcomes did not explain much of the variation in fatigue ([Formula: see text] = 0.12), while subjective outcomes had a strong negative impact and partly explained the variation in fatigue ([Formula: see text]= 0.27). Country of residence had a significant additional effect (increasing model fit to [Formula: see text] = 0.20 and [Formula: see text] = 0.36, respectively). Remarkably, higher GDP and better HDI were associated with higher fatigue, and explained a large part of the country effect. Logistic regression confirmed the limited contribution of objective outcomes and the relevant contribution of country of residence.
  
  
  CONCLUSIONS
  Country of residence has an important influence on fatigue. Paradoxically, patients from wealthier countries had higher fatigue.
authors.affiliation: Rheumatology, Maastricht University Medical Center, CAPHRI, Maastricht, Department of Internal Medicine, Maastricht University Medical Centre, monikahifinger@gmx.de.
authors.forename: Monika
authors.initials: M
authors.lastname: Hifinger
authors.affiliation: Rheumatology, Maastricht University Medical Center, CAPHRI, Maastricht, Health Promotion, Maastricht University, CAPHRI, Maastricht.
authors.forename: Polina
authors.initials: P
authors.lastname: Putrik
authors.affiliation: Rheumatology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Sofia
authors.initials: S
authors.lastname: Ramiro
authors.affiliation: Medical Informatics, Uniklinik RWTH Aachen University, Aachen, Germany.
authors.forename: András P
authors.initials: AP
authors.lastname: Keszei
authors.affiliation: Mohammed V University, Faculty of Medicine, Laboratory of Clinical Research and Epidemiology, Rheumatology Department, El Ayachi Hospital, Rabat, Morocco.
authors.forename: Ihsane
authors.initials: I
authors.lastname: Hmamouchi
authors.affiliation: Paris Descartes University, Rheumatology Department, Cochin Hospital, Assistance Publique-Hôpitaux de Paris, INSERM (U1153): Clinical Epidemiology and Biostatistics, PRES Sorbonne, Paris-Cité and.
authors.forename: Maxime
authors.initials: M
authors.lastname: Dougados
authors.affiliation: Department of Rheumatology, Sorbonne Universités, UPMC Univ Paris 06, Institut Pierre Louis d' Epidémiologie et de Santé Publiquez, GRC-UPMC 08 (EEMOIS); AP-HP, Pitié Salpêtrière Hospital, Paris, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Gossec
authors.affiliation: Rheumatology, Maastricht University Medical Center, CAPHRI, Maastricht, Department of Internal Medicine, Maastricht University Medical Centre.
authors.forename: Annelies
authors.initials: A
authors.lastname: Boonen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000150:complications* / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005221:Fatigue / Q000453:epidemiology / Q000209:etiology*; D005260:Female; D059066:Gross Domestic Product / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D012111:Residence Characteristics; D012720:Severity of Illness Index; D012959:Socioeconomic Factors; D055815:Young Adult
keywords: COMORA; cultural aspects; disease activity; fatigue; inequalities; multinational study; rheumatoid arthritis