Coronaviruses are a group of lipid containing, enveloped RNA viruses with distinctive surface projections (44, 53, 65). They cause serious infections in many animal species, including hepatitis and encephalitis in mice, bronchitis in chickens, encephMomyelitis in piglets and severe gastroenteritis in neonatal calves, piglets and dogs. In contrast, all of the more than 20 coronavirus strains so far positively isolated from man are in association with mild upper respiratory tract infections.

Since 1975, a number of reports have identified coronavirus-like particles (CVLPs) in faecal specimens from adults and children suffering from gastro-enteritis and also from healthy subjects: these have been summarized previously (21, 29, 40). Similar particles have been found in faecal samples from a number of animals. In all these studies, the presence of CVLPs was not clearly associated with disease and the particles were characterized as coronavirus-like entirely on their morphology, particularly the possession of surface projections approximately 20 nm long. The particles were pleomorphic and usually much larger than coronaviruses grown in cell culture. Although many attempts have been made to grow human CVLPs in organ and tissue cultures, all attempts have failed with the exception of two laboratories which have reported their growth either in organ cultures (ll, 12) or in tissue cultures (35, 61), but both these reports require confirmation.