[Study of an outbreak of hysteria after hepatitis B vaccination].

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.

SUBJECTS AND 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.