A critical review of the Pfiesteria hysteria hypothesis.

Mass hysteria or mass psychogenic illness is the spread of the belief of an illness (symptoms and the origins of the symptoms) through a population. The characteristics of mass psychogenic illness were reviewed and compared to the recent outbreak of human illness in the Pocomoke region in Maryland in the summer of 1997. The findings suggest that the nature of the symptoms complex--the onset and recovery course; the absence of secondary gain or job-related stress for most of the symptomatic persons; the predominance of males in the symptomatic group; and the baseline emotional stability of all persons examined--are inconsistent with the reported features of psychogenic illness in response to unknown environmental or chemical toxins. Although there may be individuals who exhibited hypochondriacal, hysterical, or other functionally based reactions, the recent outbreak of Pfiesteria-related illness probably does not represent an episode of mass psychogenic illness.