Ontario researchers seek 50,000 participants to study impact of COVID-19 on the brain Including cases in Europe, where it was first reported, about 1,000 children worldwide have been affected, a journal editorial said.The federal Centers for Disease Control and Prevention’s case definition includes current or recent COVID-19 infection or exposure to the virus; a fever of at least 100.4 for at least 24 hours; severe illness requiring hospitalization; inflammatory markers in blood tests, and evidence of problems affecting at least two organs that could include the heart, kidneys, lungs, skin or other nervous system.Digestive symptoms including nausea and diarrhea are common.