European health officials say they have not found a link between cases of a mysterious liver disease outbreak in children.

Around 190 cases have been reported worldwide, of which 140 are in Europe. Andrea Ammon, Director at the European Centre for Disease Prevention and Control said Tuesday there is so far “no connection between the cases.”

She said the hepatitis of unknown origin has appeared in European countries, Israel and the United States.

The disease has affected children who were previously healthy.

On Saturday, the World Health Organization said that at least one death has been reported.

The U.N. health agency didn’t say in which country the death occurred.

Other cases have led to acute liver failure, which required a transplant.

Experts say the disease may be linked to a virus associated with colds, but more research is needed.