Calicivirus detected in outbreaks of acute gastroenteritis in school children.

Outbreaks of acute gastroenteritis occurred in AK and N Primary Schools of Osaka Prefecture early in March and early in November, respectively, 1977. Epidemiological surveys were carried out in both schools with the following results. The morbidity rates were 21.8% (AK) and 8.5% (N) among all pupils, and 41.7% (AK) and 36.8% (N) in special age groups. The main clinical symptoms were abdominal pain (77.2-91.3%), diarrhea (38.4-41.3%) and vomiting (6.5-41.6%). Electron microscopic observations of negatively stained specimens showed that five of 15 fecal extracts obtained from patients in the two schools contained virus particles of 35-40 nm diameter with some black hollows on the surface of complete particles and ten projection-like structures at the edge of empty shells. These morphological characteristics resemble those of calicivirus particles. Immune electron microscopic examination suggested that outbreak in AK School was associated with this virus. Attempts to cultivate the viruses in various cultured cells and in suckling mice were unsuccessful.