From mid-July through late September 1970, 221 persons developed an illness characterized by acute gastroenteritis, myalgias, and lethargy. Encephalopathy became evident in 18 patients. The latter was relapsing and had a slow convalescence. Physical findings were few, and laboratory examinations were not helpful in establishing a diagnosis. This epidemic appears to be a variant of so-called "epidemic neuromyasthenia," which may be more common than medical literature would indicate.
Graybill JR, Silva J, O'Brien MS, Reinarz JA. Epidemic NeuromyastheniaA Syndrome or Disease?. JAMA. 1972;219(11):1440-1443. doi:10.1001/jama.1972.03190370032007