The World Health Organization has confirmed that at least one child has died from a mystery strain of severe hepatitis which has now been reported in 12 countries.
There are 169 cases of acute hepatitis in young children that the UN body is aware of. 17 became so sick that they needed transplants.
The UK has 114 infections, followed by Spain with 13 and Israel with 12. The outbreak has spread to the US, Ireland, the Netherlands, Italy, France, Norway, and Belgium.
Severe hepatitis in previously healthy children is rare.
The mystery illness has affected young people ranging from one month to 16 years old and has been investigated by health authorities.
The WHO encouraged countries to report similar cases in an interview with Stat.
The consequences have been quite severe, according to Richard Pebody of the WHO European division.
The cases are not related to any of the typical strains of the virus.
Scientists believe that an adenoviruses, a common type of virus that can cause common colds, could be behind the wave of acute hepatitis cases. At least 74 children have tested positive for adenoviruses.
Adenoviruses 41 has been linked to the disease in children with immunocompromised children, but it has never been shown to cause the disease in previously healthy children.
Public Health Scotland's director, Jim McMenamin, told the news agency that work is under way to understand if an adenoviruses has changed to cause more severe disease or if it could be causing the problems.
According to the WHO, the vast majority of children who have fallen ill were not vaccinations.
Scientists said that reduced social mixing during the Pandemic could be an explanation for lowered immunity.
There are a number of symptoms of the disease, including dark urine, yellow eyes and skin, sickness, fatigue, fever, loss of appetite, nausea, vomiting, abdominal pain, light-coloured stools and joint pain.
Parents are being told to look out for symptoms and to contact a healthcare professional if they are concerned about their child. The British Health Security Agency encourages hand washing and proper respiratory hygiene, such as catching coughs and sneezes in a tissue.