According to health officials, cases of hepatitis, or liver inflammation, have been reported in Denmark, Ireland, the Netherlands, Spain, and the United States.
Last week, UK health officials announced that they had discovered a higher-than-usual number of cases of the infection among children.
The cause of the infections is unknown at this time.
The European Centre for Disease Control (ECDC) did not specify how many cases were discovered in total across the four European countries.
It was also stated that investigations into similar cases are being conducted in other states.
The United Kingdom has reported the most cases, with a total of 74 reported so far.
The usual viruses that cause infectious hepatitis (hepatitis A to E), according to the UK Health Security Agency, have not been detected among the cases in the UK.
As a result, researchers are looking into other possible causes and believe that the common adenovirus could be the culprit.
Adenoviruses are a type of virus that causes a variety of minor illnesses such as colds, vomiting, and diarrhoea.
It did, however, state that other possible causes of the infection are being investigated, and that Covid-19 had not been ruled out. It went on to say that there is no apparent link to Covid-19 vaccines.
What exactly is hepatitis?
It is a broad term used to describe liver inflammation.
It is usually caused by a viral infection, but it can also be caused by chemical exposure, excessive alcohol consumption, drugs, and certain genetic disorders.
There are five types of hepatitis caused by specific viruses, known as A, B, C, D, and E, but none of them appear to have caused the liver inflammation seen in these children thus far.
Some types of hepatitis are short-lived, while others can be life-threatening.
Parents in the United Kingdom should be on the lookout for symptoms such as jaundice, according to health officials.