Background: Mass psychogenic illness refers to outbreaks of illness attributed to a toxic agent but for which no plausible organic cause is found. We determined the frequency and predictors of mass psychogenic illness within a sample of chemical incidents.
Methods: Information was collected on a random sample of 280 chemical incidents. We developed consensus operational criteria for mass psychogenic illness and estimated its frequency. We then assessed environmental, emergency, and health service indicators for their association with mass psychogenic illness.
Results: Nineteen “chemical incidents” were probable episodes of mass psychogenic illness. This represented 16% of incidents for which people reported symptoms and 7% of all incidents. Odor was a robust predictor of mass psychogenic illness. These illnesses were especially likely to occur in schools or healthcare facilities.
Conclusions: A substantial minority of chemical incidents may be mass psychogenic illness.
From the aDivision of Psychological Medicine, Institute of Psychiatry, King's College London, London, United Kingdom; and bCentre for Radiation, Chemical and Environmental Hazards, Health Protection Agency, London, United Kingdom.
Submitted 23 November 2009; accepted 9 March 2010.
Supported by the UK Home Office CBRN Science and Technology Programme (study reference: 43/05/81) (to C.K.); the National Institute of Environmental Health Sciences (NIEHS), National Institute of Health as a Ruth L Kirschstein National Research Fellow (F32 ES013690) (to L.A.P.); the South London and Maudsley NHS Foundation Trust/Institute of Psychiatry National Institute of Health Research (NIHR) Biomedical Research Centre (to S.W.). The Health Protection Agency was a cosponsor.
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Correspondence: Lisa A. Page, Division of Psychological Medicine, Institute of Psychiatry, Weston Education Centre, Room 3.14, KCL, 10 Cutcombe Rd, London SE5 9RJ, United Kingdom. E-mail: email@example.com.