OBJECTIVE: In April 1989 an outbreak of illness suddenly afflicted student performers in Santa Monica, Calif., and an extensive investigation revealed no environmental cause. To clarify the details of the epidemic and determine whether mass hysteria occurred, the authors examined physical, psychological, and social factors that might have contributed to the outbreak. METHOD: Participating middle- and high-school performers were surveyed; 93% (N = 519) responded; cases were defined as students who had one or more symptoms during the outbreak. A stepwise logistic regression analysis was used to determine significant predictors of illness. RESULTS: Characteristic features of mass hysteria were present, including preponderance of illness in girls, symptom transmission by sight or sound, presence of hyperventilation, and evidence of psychological or physical stress. Symptomatic and asymptomatic groups differed in frequency of several physical and psychological variables, but observing a friend become sick was the best predictor of the development of symptoms. CONCLUSIONS: These results confirm earlier research demonstrating multiple psychological and physical factors that contribute to such outbreaks, particularly symptom transmission through social networks. Investigators should explore social transmission as an additional characteristic feature of mass hysteria in order to facilitate early identification of future outbreaks.
OBJECTIVE: In April 1989 an outbreak of illness suddenly afflicted student performers in Santa Monica, Calif., and an extensive investigation revealed no environmental cause. To clarify the details of the epidemic and determine whether mass hysteria occurred, the authors examined physical, psychological, and social factors that might have contributed to the outbreak. METHOD: Participating middle- and high-school performers were surveyed; 93% (N = 519) responded; cases were defined as students who had one or more symptoms during the outbreak. A stepwise logistic regression analysis was used to determine significant predictors of illness. RESULTS: Characteristic features of mass hysteria were present, including preponderance of illness in girls, symptom transmission by sight or sound, presence of hyperventilation, and evidence of psychological or physical stress. Symptomatic and asymptomatic groups differed in frequency of several physical and psychological variables, but observing a friend become sick was the best predictor of the development of symptoms. CONCLUSIONS: These results confirm earlier research demonstrating multiple psychological and physical factors that contribute to such outbreaks, particularly symptom transmission through social networks. Investigators should explore social transmission as an additional characteristic feature of mass hysteria in order to facilitate early identification of future outbreaks.