Epidemic

Epidemic,
early 17th century (as an adjective): from French épidémique, from épidémie, via late Latin from Greek epidēmia ‘prevalence of disease’, from epidēmios ‘prevalent’, from epi ‘upon’ + dēmos ‘the people’.Google.
"Vigorous endeavours by authorities had failed to discover the offending agent. By the use of epidemiological methods, the present study attempted to investigate the nature of and the significant contributing factors related to the episode. The psychological nature was confirmed both by demonstration of positive characteristics as well as by the exclusion of organicity. "-- Psychological epidemic ... S W Wong, et al, 1982
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Psychological transmission
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