Mass Psychogenic Illness: Can Experts Agree When It Occurs and How Often?

Abstract

ISEE-0416 Background & Objective: Mass Psychogenic Illness, sometimes known as mass hysteria, can been defined as: “widespread, subjective symptoms thought to be associated with environmental exposure to a toxic substance in the absence of objective evidence of an environmental cause” [1]. Over 200 case reports have been published on such episodes, but rarely does the literature go beyond that of the simple case study. The aim of this research was to test consensus criteria on how to define this intriguing phenomenon and to determine its frequency. Methods: Three independent experts in toxicology were asked to rate 280 chemical incidents against consensus criteria for Mass Psychogenic Illness. The criteria have been developed by our group for practical and research use. The incidents were selected sequentially and prospectively from a surveillance system run by the Chemical Hazards and Poisons Division of the Health Protection Agency, UK. Incidents for which the independent toxicologists agreed met all our criteria were designated as being due to Mass Psychogenic Illness. The prevalence and predictors of these incidents were then estimated. Results: Using our criteria, toxicologists were able to agree on which incidents were Mass Psychogenic in origin. Preliminary results show that 13 (4.6%) of incidents were likely to be examples of Mass Psychogenic Illness. Such incidents were more likely to be associated with an odour, OR = 5.0 (95%CI 2.4-10.4), and with high use of emergency health resources e.g. receiving large number of casualties, OR = 4.8 (95%CI 1.8-12.9), and activation of hospital major incident plans. Conclusion: Operational criteria for the definition of Mass Psychogenic Illness enable toxicologists to identify such episodes from a brief case description. These episodes are not uncommon and are likely to be associated with high costs to health and emergency services. Further work on early identification and successful management of these incidents is required.