It is not yet clear what caused the hepatitis infections. Health authorities say there are no foreign travel or other underlying factors that would put the children at greater risk.
They do see a sharp increase in infections with adenoviruses, ie viruses that cause respiratory infections. There are dozens of types of adenoviruses, most of which are accompanied by symptoms of a cold, fever and sore throat. But some variants lead to other problems, such as stomach and intestinal inflammation. Adenoviruses have previously been linked to hepatitis in children, but mainly in children with weakened immune systems.
The children in the United States all tested positive for an adenovirus. Of the children who got sick in Europe, some tested positive for an adenovirus, others for the coronavirus. The WHO emphasizes that much more research is needed into any possible link to specific viruses.