German health authorities say at least 4,000 children have fallen ill with vomiting and diarrhea after eating food from school canteens and daycare centers.
The Robert Koch-Institut says it was alerted to a sudden surge in gastroenteritis cases that began late Tuesday in Berlin and surrounding regions.
The institute said in a statement late Thursday that laboratory investigations are under way to determine the exact cause of the outbreak.
But it says all facilities where the illness occurred likely received food from a single supplier, indicating it was a food-borne illness such as norovirus.
The norovirus is a common cause of food poisoning.