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Acute infectious nonbacterial gastroenteritis was induced in adult volunteers through three serial passages by oral administration of bacteria-free stool filtrates. This suggested that a replicating agent of subbacterial size was responsible for the observed disease. The biophysical properties of the agent, as assayed in volunteers, were consistent with those of a small virus, most closely related to the parvovirus group among known animal viruses. The agent appeared to have a diameter less than 66 nm and likely less than 36 nm. It appeared to lack a lipid containing envelope and was acid stable. It was stable to heating at 60° for 30 min. The agent appeared to be relatively host specific for man and conferred at least short-term immunity. Because of the high frequency of disease induced in unselected volunteers, widespread natural immunity to this agent may be absent or perhaps incomplete. Preliminary evidence suggested that the Norwalk agent replicated in an in vitro system, human fetal intestinal organ culture.
Dolin et al. (1972) studied this question.