These cases of severe liver inflammation are also raising concerns in Europe, where many cases have also been detected, and scientists around the world are working to understand the cause.

In the United States, cases have been identified in 25 states and territories, and affected children have a median age of just 2 years, said an official from the Centers for Disease Control and Prevention (CDC) during a a press conference.

Because of their young age, the children concerned were for the most part not eligible to be vaccinated against Covid-19.

"Vaccination against Covid-19 is not the cause" of this disease, hammered Jay Butler, deputy director in charge of infectious diseases for the CDC, saying he wanted to put an end to rumors circulating on the internet.

He clarified that the Covid-19 infection itself was not however ruled out as a potential cause.

However, the CDC favors the trail of a certain type of adenovirus -- viruses that are fairly common, but which have not previously been known to cause cases of hepatitis in healthy children.

It has been confirmed that more than half of the children affected in the United States have tested positive for the so-called "type 41" adenovirus, hitherto better known for causing gastroenteritis.

This adenovirus has also been detected in many affected children outside the United States.

One of the hypotheses is that the reaction to this adenovirus may be disrupted by another factor, such as infection with Covid-19 or environmental factors, for example contact with animals or a toxin.

"Investigators here and around the world are working hard to determine the cause," said Jay Butler.

Liver transplants

Parents are encouraged to watch for any symptoms in their children (vomiting, dark urine, pale stools, jaundice, etc.), and to contact their doctor if they have concerns.

Two weeks ago, the CDC issued a health alert for doctors to notify authorities of any suspected cases of hepatitis of unknown origin.

The 109 detected cases occurred over the past seven months, Butler said.

And 14% of affected children had to receive a liver transplant.

If 90% of the children had to be hospitalized, in the majority of cases they recovered afterwards.

"We know that this news can be worrying, especially for parents of young children. It is important to remember that this severe hepatitis is rare," wanted to reassure Mr. Butler.

He said that the number of pediatric emergency room visits for hepatitis was not currently abnormally high in the United States, unlike the United Kingdom.

Some 163 cases have been identified in the United Kingdom, British health authorities announced on Friday.

Outside the United States, at least more than 200 cases have been identified, another CDC official said.

© 2022 AFP