A vomiting bug has been reported at an international Jamboree on the outskirts of Norwich.
Norjam, which hosts thousands of adults and children from scout and guide associations from around the world, said 41 people had visited its onsite medical centre.
No one has been taken to hospital and Public Health England (PHE) has been informed, it added.
PHE said it was providing hygiene and infection control advice to help stop the illness spreading.
The week-long Jamboree at the Norfolk Showground ends on Saturday.