Acute hepatitis — or inflammation of the liver — among children was first reported in the UK last week.
Health authorities in four European countries and the United States are investigating records of hepatitis in children.
Cases of hepatitis, or inflammation of the liver, have been reported in Denmark, Ireland, the Netherlands, Spain and the US. And UK health officials said last week they had detected more than usual cases of the infection among children.
The cause of the infections is not yet known.
The European Center for Disease Control (ECDC) did not specify how many cases were found in the four European countries in total.
But the World Health Organization (WHO) said fewer than five were found in Ireland and three in Spain. He added that detection of more cases in the coming days is likely.
Investigations into the cause of the infections are ongoing in all European countries where cases have been reported, the ECDC said.
In the US, the Alabama Department of Public Health said nine cases had been detected in children aged one to six years old, with two of them needing liver transplants. Investigations of similar cases in other states are ongoing.
The UK is where the highest number of cases have been reported, with a total of 74 so far.
Last week, the UK Health Safety Agency said the usual viruses that cause infectious hepatitis (hepatitis A to E) were not detected among cases in the UK.
As a result, professionals are looking at other possible causes and believe the common adenovirus could be the cause.
Adenoviruses are a family of viruses that commonly cause a range of mild illnesses such as colds, vomiting and diarrhea.
However, other possible causes of the infection are also being investigated, including Covid-19.
Officials said there was no apparent link to Covid-19 vaccines.
What is hepatitis?
Hepatitis is a broad term used to describe inflammation of the liver.
It is usually caused by a viral infection. But the disease can also be brought on by exposure to some chemicals, excessive consumption of alcohol, drugs, and certain genetic disorders.
There are five main types of hepatitis caused by specific viruses known as A, B, C, D and E, but none of them seem to have caused the liver inflammation seen in these children so far.
Some types of hepatitis can go away without serious problems, while others can be long-lasting.
UK health officials said parents should be on the lookout for symptoms such as jaundice (yellowing of the skin and whites of the eyes).