At least 650 cases of abrupt and unexplained hepatitis in young children are being investigated in 33 countries, an increase of roughly 36 cases since the last international update, about a week ago. Another 99 instances are still being classified, according to the World Health Organization.

The European Centre for Disease Prevention and Control reported 614 cases under investigation in 30 countries last week.

Around one-third of the cases, 222, have been confirmed in the United Kingdom, with another 216 reported in the United States, according to WHO. According to the update, the majority of the children in the international probe became ill in March and April.

Prior to this outbreak, around half of all occurrences of acute hepatitis — or liver inflammation — in young infants could not be linked to a recognized cause. However, according to WHO, the cases being investigated today appear to be unlike anything doctors have seen previously.

More clinically severe Hepatitis 

Hepatitis appears to be more clinically severe, with a higher proportion of children experiencing liver failure. A sample of 156 cases with data on hospital admission required critical care, and 12% required a liver transplant.

According to the WHO, it is unclear whether there are more cases of sudden hepatitis than doctors would ordinarily anticipate observing during the same time span.
 
The majority of the children affected (75%) are under the age of five. Most were in good health before becoming ill. Common hepatitis viruses, such as hepatitis A, B, C, D, and E, have been ruled out in these children.

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Adenovirus 41

The strongest link between the cases appears to be adenovirus 41, which is known to cause an upset stomach such as diarrhea and vomiting; many of the affected children reported those symptoms before becoming jaundiced, which occurs when the whites of their eyes and possibly their skin develop a yellowish tinge, which is a sign of liver problems.

Experts say adenovirus 41 is unlikely to be the culprit because it has never been linked to hepatitis in youngsters with healthy immune systems.

SARS-CoV-2

The UK Health Security Agency has undertaken a case-control study to see if adenovirus 41 is more prevalent in children with hepatitis than in others. According to UK researchers, there has been a surge in adenovirus activity, which is co-circulating with SARS-CoV-2, the virus that causes Covid-19.

SARS-CoV-2 has been found in a number of patients, according to WHO, albeit data is limited.

Other suspected reasons being investigated by researchers include environmental exposures, chemicals, and maybe co-infections with another virus.

Investigators in the United Kingdom have ruled out dog contact as a possible cause in these cases, and because the majority of the youngsters are too young to be vaccinated against Covid-19, they believe the Covid vaccines are ineffective.