In the United States, an unexpected number of children have contracted a severe form of hepatitis.
The top health authority (CDC) called on the country's doctors on Thursday to test young patients with liver inflammation for the adenovirus, which may be responsible for the wave of the disease.
Last November, a children's hospital in the state of Alabama reported five children with severe liver inflammation and adenovirus infections.
Three of the patients, aged up to six years, were diagnosed with acute liver failure and two required a transplant.
In the weeks that followed, four more children contracted severe hepatitis.
According to the Centers for Disease Control and Prevention, hepatitis in healthy children is usually mild.
The difficult course in Alabama is therefore striking.
The state of North Carolina has also registered several cases of severe liver inflammation in connection with the highly contagious adenovirus, which causes infections in the eyes, respiratory tract and gastrointestinal tract.
"We haven't been able to find a clear cause or a common set of circumstances under which the children became infected," Bailey Pennington, a spokeswoman for the North Carolina Department of Health, told NBC.
According to previous studies by the American authorities, the liver inflammation, which has also been found in children in Great Britain, Spain and Denmark, is not related to Corona.
None of the young patients in Alabama had contracted or been vaccinated against the virus prior to hepatitis.