Poor food hygiene may have caused more than 90 children to fall ill at Tavatui recreation camp in the Sverdlovsk region, investigators said Monday.
Other possible causes have not yet been excluded, but investigators think the children could have come into contact with a virus carried contained in contaminated water or on poorly washed fruit and vegetables, Interfax reported.
Investigators have spoken to kitchen staff and other employees at the camp, none of whom fell ill despite living and dining alongside the children. All of the reported cases took place in children between the ages of 7 and 15.
Following the outbreak last Friday, 37 children were taken to a medical facility in the nearby town of Novouralsk, 25 were taken home by their parents, 21 were sent to Yekaterinburg and a further five were interned at the camp's infirmary.
More than 200 children who were not affected by the illness were transported back from the camp to their homes.
Speaking Friday, local health officials said they had everything they needed to assist the affected children, while regional authorities said they would check all other children's camps in the region to prevent similar incidents from occurring.