title: [Study of an outbreak of hysteria after hepatitis B vaccination].
abstract: BACKGROUND
  The aim of this study was to describe an epidemic outbreak of mass hysteria among adolescents which occurred after the immunisation with vaccine against hepatitis B and to determine the association with social variables related to the students.
  
  
  METHODS
  All the available information was evaluated and a questionnaire was designed, which included sociodemographic, clinics and school environment variables. A case-control study was conducted. The data were analyzed and outbreak rate and odds ratio with their respective CI (95%) were calculated.
  
  
  RESULTS
  18 cases (among a set of 74 students of seventh of EGB) were clustered in time (10.30-11 h) and space (class of seventh B). There was a clear association between the cases and the female sex (odds ratio = 5.4; CI 95% 1.3 - 23.8). As for the sociological variables there was a association with increasing household members (odds ratio = 5.3; CI 95% 1.3 - 23.4) and with lower educational levels of the father (odds ratio = 10.6; CI 95% 1.2 - 239.9). Among the affected a more unfavorable opinion of the school was detected.
  
  
  CONCLUSIONS
  This outbreak fulfils 8 of the 11 criteria classically admitted as usual characteristics of a mass psychogenic illness episode. The sensorial transmission remains demonstrated supporting the hypothesis of a chain reaction.
authors.affiliation: Centro Nacional de Epidemiología, Instituto de Salud Carlos III, Ministerio de Sanidad y Consumo, Madrid.
authors.forename: E F
authors.initials: EF
authors.lastname: Peiró
authors.forename: J L
authors.initials: JL
authors.lastname: Yáñez
authors.forename: I
authors.initials: I
authors.lastname: Carramiñana
authors.forename: J V
authors.initials: JV
authors.lastname: Rullán
authors.forename: J
authors.initials: J
authors.lastname: Castell
mesh_terms: D000293:Adolescent; D000367:Age Factors; D016000:Cluster Analysis; D004196:Disease Outbreaks; D005260:Female; D017325:Hepatitis B Vaccines; D006801:Humans; D007046:Hysteria / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D016017:Odds Ratio; D012737:Sex Factors; D012959:Socioeconomic Factors; D013030:Spain / Q000453:epidemiology; D011795:Surveys and Questionnaires; D014611:Vaccination
chemical_list: D017325:Hepatitis B Vaccines
vernacular_title: Estudio de un brote de histeria después de la vacunación de hepatitis B.