The 33- to 39-nm virus-like particles, tentatively designed as Sapporo agent, associated with an outbreak of acute gastroenteritis.

An outbreak of nonbacterial gastroenteritis occurred in an orphanage in December 1979. Of 54 residents, 43 were affected with acute gastroenteritis. Diarrhea was the commonest symptom. The 33- to 39-nm virus-like particles, tentatively designated as Sapporo agent, were detected in 17 (48.6%) of the patients' 35 fecal specimens. Morphologically, it was difficult to distinguish the Sapporo agent from other agents without geometrical pattern of the surface. Antigenically, the Sapporo agent related to the Otofuke agent detected in an outbreak of the institution for mentally retarded adults and also to the SRV ;76 detected in familial cases of infectious gastroenteritis. The Sapporo agent might belong to a new group of those gastroenteritis viruses which were larger in size than the Norwalk virus group.