Almost a third of pupils at a primary school in Leicestershire have missed classes because of a sickness bug.
More than 100 children were off sick from Little Bowden Primary School in Market Harborough at the peak of the outbreak.
The bug is characterised by vomiting and diarrhoea.
The virus is thought to have been spread when a sick child attended a school disco last Friday, school officials said.
Vigorous strain
School netball and football matches had to be cancelled to stop the bug from spreading to other schools.
Headteacher Bleddyn Jones said: "I have been a head teacher for 20 years and I have never seen anything like it ever before.
"It completely took us by surprise.
"On Monday the phone was red hot with calls for parents saying children were ill with stomach bugs.
"It was frightening and unnerving but the health officials told us there was no need to shut down."
The bug is not believed to have spread to other schools in the area.
Some classes were reduced to single figures early in the week, but most children have returned to school, Mr Jones said.