OBJECTIVE: To clarify factors contributing to mass illness of sudden onset by studying an outbreak that was apparently triggered by a gaseous odor and that involved a rapid, extensive response by school and fire officials. SETTING: Urban elementary school. MAIN OUTCOME MEASURE: A standardized student questionnaire was designed to identify potential illness predictors. DESIGN: Four weeks following the outbreak, public health officials distributed the questionnaire to all students in regular classes in grades 3 through 6 (N = 319), representing 46% of the estimated 680 students present the day of the outbreak. RESULTS: Seventy-seven percent of the students who completed the questionnaire reported that they experienced physical symptoms during the epidemic. A stepwise regression analysis demonstrated several independent variables that predicted the severity of illness, including the intensity of the odor smelled during the outbreak (P < .0001), becoming sick after the fire trucks arrived (P < .0001), and believing in an environmental cause for the illness (P < .002). CONCLUSIONS: These results indicate that both psychological and environmental factors, real or perceived, may contribute to sudden-onset epidemics of hysteria. Moreover, the response intervention of officials may influence the extent of such outbreaks. Early recognition of psychological causes and dispersion of groups at risk could reduce morbidity and associated health care costs.
OBJECTIVE: To clarify factors contributing to mass illness of sudden onset by studying an outbreak that was apparently triggered by a gaseous odor and that involved a rapid, extensive response by school and fire officials. SETTING: Urban elementary school. MAIN OUTCOME MEASURE: A standardized student questionnaire was designed to identify potential illness predictors. DESIGN: Four weeks following the outbreak, public health officials distributed the questionnaire to all students in regular classes in grades 3 through 6 (N = 319), representing 46% of the estimated 680 students present the day of the outbreak. RESULTS: Seventy-seven percent of the students who completed the questionnaire reported that they experienced physical symptoms during the epidemic. A stepwise regression analysis demonstrated several independent variables that predicted the severity of illness, including the intensity of the odor smelled during the outbreak (P < .0001), becoming sick after the fire trucks arrived (P < .0001), and believing in an environmental cause for the illness (P < .002). CONCLUSIONS: These results indicate that both psychological and environmental factors, real or perceived, may contribute to sudden-onset epidemics of hysteria. Moreover, the response intervention of officials may influence the extent of such outbreaks. Early recognition of psychological causes and dispersion of groups at risk could reduce morbidity and associated health care costs.