Tests have confirmed norovirus was the cause of 90 children from a kindergarten in Minhang District becoming ill on Tuesday night, the Children's Hospital of Fudan University said yesterday.
The virus was found present in samples of vomit from the sick children and the investigation ruled out the possibility of food poisoning, hospital officials told Shanghai Daily.
A joint investigation was launched on Tuesday by the district's disease control center and education and market supervision bureaus, after the center was told several children from the same school had started vomiting.
The source of the virus is still under investigation. Medical experts said the outbreak may have been caused by contaminated food or water.
The highly contagious virus has a small range for spreading by air and staff at kindergartens and schools have been trained to separate sick children to prevent infecting others.
"Usually, if we do right in personal hygiene, food safety and health monitoring for workers dealing with food, we can basically prevent such large-scale spread," said Zeng Mei, director of the infectious diseases department of the Children's Hospital.
"The norovirus is highly contagious and outbreaks are common in cold seasons, such as winter and early spring," Zeng said. "There is a cold spell in late spring this year, so the virus is active.
"This is why several schools and kindergartens have reported norovirus cases recently."