title: The epidemiology of chronic fatigue in the Swedish Twin Registry.
abstract: BACKGROUND
  Chronic fatigue syndrome (CFS) remains an idiopathic and controversial entity.
  
  
  METHODS
  We screened 31405 individual members of the Swedish Twin Registry (aged 42-64 years) for the symptoms of fatiguing illness via a telephone questionnaire. We refined self-reported symptoms via data from several national registries and from physician review of all available medical records in order to approximate closely the dominant case definition of CFS.
  
  
  RESULTS
  The 6-month prevalence of CFS-like illness was 2.36% (95% CI 2.19-2.53) and was markedly higher in women than men, odds ratio 3.92 (95% CI 3.24-4.72) with no significant association with age or years of education. There was a highly significant association with occupation that disappeared after accounting for gender.
  
  
  CONCLUSIONS
  CFS-like illness may be more common that previously acknowledged. There is a marked increase in risk by gender. Previous reports that CFS is more prevalent in individuals in certain occupational categories were not confirmed and may have been due to confounding by gender.
authors.affiliation: Department of Laboratory Medicine, Karolinska Institutet at Karolinska University Hospital Huddinge, Stockholm, Sweden.
authors.forename: Birgitta
authors.initials: B
authors.lastname: Evengård
authors.forename: Andreas
authors.initials: A
authors.lastname: Jacks
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: Patrick F
authors.initials: PF
authors.lastname: Sullivan
mesh_terms: D000328:Adult; D015673:Fatigue Syndrome, Chronic / Q000453:epidemiology* / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009790:Occupations; D016017:Odds Ratio; D015995:Prevalence; D012737:Sex Factors; D013548:Sweden / Q000453:epidemiology