A total of 56 children from 17 schools are gravely ill in hospital after mass poisoning by rats or mice.
Health officials say the students ate vegetables suspected of being infected by rodent droppings or urine.
The youngsters in Russia, aged seven to 14, are suffering from high fever, rashes, swelling, redness, vomiting and diarrhoea.
One schoolboy Nikita, nine, said: “My stomach ached badly, and I could not eat and walk.”
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In all, 91 were infected with dozens in a “moderately grave” condition in infectious diseases hospitals, according to reports in Krasnoyarsk.
Health watchdog Rospotrebnadzor said the children had become infected with yersiniosis after eating salad in their school canteens.
Infections diseases doctor Ilya Akinfiev feared the school food had been on surfaces contaminated with excrement or urine from rodents.
Dr Akinfiev said: “This happens, for example, if their urine gets on cutting boards or the surfaces of tables where food is being prepared.”
Children are still suffering from infections two weeks after the contamination.
Mother Yulia Verevkina said: “It is from the suppliers.
"Rodents, mice, ran over the fruits and vegetables and this is the cause of it.”
Another mother Kristina Shultseva said: “Schools failed to wash the vegetables properly, so the infection spread.”
The schools hit by infections all used the same food supplier, it is understood.
A formal investigation by the regional state prosecutor’s office has been opened into the poisoning.
Rospotrebnadzor spokeswoman Natalya Krasnopeeva said: “A temporary ban was imposed on the food supplier."