The World Health Organization has reported that it has received 650 reports of probable cases of acute hepatitis in children till May 26, 2022. However, the cause of these cases still remains ambiguous and is under investigation. These cases are reported from 33 countries, with 99 additional cases awaiting classification. 

As per US health authorities, adenovirus infection is the leading cause of severe hepatitis of unknown origin in children. Hepatitis linked to adenovirus is also exclusively seen in immunocompromised children. 

The US CDC has also said that investigations are ongoing to find out whether the hepatitis cases may have any link to COVID-19 infections along with other pathogens, medications, and risk factors. 

[Source Link: WHO says 650 probable cases of acute child hepatitis reported so far | Reuters]