The human small and large intestine were studied for viruses, bacteria, and fungi in 29 adults with acute diarrheal disease. No etiologic agent was found in 83% of the cases. The most striking finding in these patients was a marked increase in the number of bacteria in the jejunal aspirates. No viruses were isolated in any of the jejunal, ileal, or fecal specimens.
Cohen R, Kalser MH, Arteaga I, Yawn E, Frazier D, Leite CA, Ahearn DG, Roth F. Microbial Intestinal Flora in Acute Diarrheal Disease. JAMA. 1967;201(11):835-840. doi:10.1001/jama.1967.03130110061015