title: The online case-crossover study is a novel approach to study triggers for recurrent disease flares.
abstract: OBJECTIVE
  To evaluate the feasibility of conducting an online case-crossover study of triggers for recurrent disease flares.
  
  
  METHODS
  We conducted an online case-crossover study of triggers for recurrent flares using gout as a paradigm. We constructed a Web site and recruited individuals with history of gout via the Internet. We confirmed gout diagnosis by reviewing each subject's medical records. We collected via the Internet exposure information during the intercritical period using a scheduled Control-period Questionnaire, and prior to recurrent gout attacks using a Hazard-period Questionnaire.
  
  
  RESULTS
  Over 10 months we recruited 197 subjects with a history of gout from 41 states and the District of Columbia. We obtained medical records from 172 subjects. All participants had experienced at least one recurrent attack and filled out required questionnaires. The median time between the date of an attack and the date of logging on to the Web site was 2 days. The incidence rate of recurrent gout attacks was 1.03 per person-year. Longer disease duration and presence of comorbidities appeared to increase the risk of recurrent flares.
  
  
  CONCLUSIONS
  The results of this study demonstrate that a case-crossover study can be successfully conducted through the Internet. This approach has broad applicability to other diseases typified by recurrent attacks.
authors.affiliation: Boston University Clinical Epidemiology Research and Training Unit, The Department of Medicine at Boston Medical Center, A203, Boston University School of Medicine, Boston, MA 02118, USA. yuqing@bu.edu
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Zhang
authors.forename: Christine E
authors.initials: CE
authors.lastname: Chaisson
authors.forename: Timothy
authors.initials: T
authors.lastname: McAlindon
authors.forename: Ryan
authors.initials: R
authors.lastname: Woods
authors.forename: David J
authors.initials: DJ
authors.lastname: Hunter
authors.forename: Jingbo
authors.initials: J
authors.lastname: Niu
authors.forename: Tuhina
authors.initials: T
authors.lastname: Neogi
authors.forename: David T
authors.initials: DT
authors.lastname: Felson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002908:Chronic Disease; D018592:Cross-Over Studies; D003625:Data Collection / Q000379:methods; D005260:Female; D006073:Gout / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D020407:Internet; D008297:Male; D008875:Middle Aged; D012008:Recurrence; D012107:Research Design; D012307:Risk Factors; D012959:Socioeconomic Factors; D014481:United States / Q000453:epidemiology