German health authorities say at least 6,500 German children and teenagers have fallen ill with diarrhea and vomiting that health authorities say has likely been caused by a foodborne virus in meals delivered to schools 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.