title: Clinical, epidemiologic, and virologic studies in four clusters of the chronic fatigue syndrome.
abstract: BACKGROUND
  The purpose of this study is to provide a case definition of chronic fatigue syndrome in an outbreak occurring in the Nevada-California region to evaluate candidate etiologic agents and observe the natural history of the illness.
  
  
  METHODS
  Patients diagnosed as having chronic fatigue syndrome were studied by repeated interviews, questionnaires, and blood collection over a 3-year period. Serum samples were tested for antibodies to Epstein-Barr virus, human herpesvirus-6, and human T-lymphotropic viruses I and II. Leukocytes from typical cases were also assayed for human T-lymphotropic viruses I and II.
  
  
  RESULTS
  Cases were defined as persons who had: (1) severe persistent fatigue following an acute illness appearing in an individual with no previous physical or psychological symptoms; (2) presenting signs and symptoms of an acute infection; (3) severe and persistent headache and/or myalgias; and (4) abrupt change in cognitive function or the appearance of a new mood disorder. After 3 years of follow-up, almost all study subjects were able to return to pre-illness activity. None of the viruses evaluated--human T-lymphotropic viruses I and II, Epstein-Barr virus, or human herpesvirus-6--could be etiologically linked to these outbreaks.
  
  
  CONCLUSIONS
  Clinical features of outbreaks of chronic fatigue syndrome differ sufficiently to suggest different etiologic agents. Giardiasis appears to have precipitated one of the four clusters in this study but the cause(s) of the other three outbreaks is as yet uncertain. The overall prognosis of chronic fatigue syndrome is usually favorable.
authors.affiliation: Environmental Epidemiology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
authors.forename: P H
authors.initials: PH
authors.lastname: Levine
authors.forename: S
authors.initials: S
authors.lastname: Jacobson
authors.forename: A G
authors.initials: AG
authors.lastname: Pocinki
authors.forename: P
authors.initials: P
authors.lastname: Cheney
authors.forename: D
authors.initials: D
authors.lastname: Peterson
authors.forename: R R
authors.initials: RR
authors.lastname: Connelly
authors.forename: R
authors.initials: R
authors.lastname: Weil
authors.forename: S M
authors.initials: SM
authors.lastname: Robinson
authors.forename: D V
authors.initials: DV
authors.lastname: Ablashi
authors.forename: S Z
authors.initials: SZ
authors.lastname: Salahuddin
mesh_terms: D000914:Antibodies, Viral / Q000097:blood*; D002140:California / Q000453:epidemiology; D016009:Chi-Square Distribution; D016000:Cluster Analysis; D004196:Disease Outbreaks / Q000706:statistics & numerical data; D015673:Fatigue Syndrome, Chronic / Q000175:diagnosis* / Q000453:epidemiology / Q000209:etiology / Q000276:immunology; D005500:Follow-Up Studies; D005873:Giardiasis / Q000150:complications / Q000175:diagnosis / Q000453:epidemiology / Q000276:immunology; D015481:HTLV-I Antibodies / Q000097:blood; D015482:HTLV-II Antibodies / Q000097:blood; D004854:Herpesvirus 4, Human / Q000276:immunology; D015654:Herpesvirus 6, Human / Q000276:immunology; D006801:Humans; D007407:Interviews as Topic; D009505:Nevada / Q000453:epidemiology; D016036:Seroepidemiologic Studies; D011795:Surveys and Questionnaires
chemical_list: D000914:Antibodies, Viral; D015481:HTLV-I Antibodies; D015482:HTLV-II Antibodies