LONDON (AP) — Scientists are investigating a puzzling spike in liver disease in children across the United Kingdom, including the cause and whether there are any links between the affected youngsters.

The U.K. Health Security Agency said this week that public health personnel are looking into 74 cases of hepatitis, or liver inflammation, detected in children since January.

The usual viruses that cause infectious hepatitis were not found in the cases, and scientists and doctors are considering other possible causes, including COVID-19, other viruses and environmental factors.

While some types of hepatitis are mild and don’t require treatment, other forms of the disease can become chronic and be fatal.

The European Centre for Disease Prevention and Control said doctors in other countries should also report potential infections in case the outbreak is not limited to Britain. It said doctors should be on the lookout for children with jaundice and symptoms including vomiting and stomach problems.

The European agency said most cases involved children ages 2 to 5. It said some children had suffered acute liver failure and a “small number have required liver transplantation.” It said there were no travel links between the affected children.

British officials said none of the affected children were vaccinated against the coronavirus, and they ruled out any links to COVID-19 vaccines.

“One of the possible causes that we are investigating is that this is linked to adenovirus infection,” said Dr. Meera Chand, director of clinical and emerging Infections at the U.K. Health Security Agency.

Adenoviruses are common viruses that cause problems like pink eye, a sore throat or diarrhea. They are often spread between people and by touching contaminated surfaces.

“The current crop of cases of hepatitis in children under the age of 10 years is very unusual,” Will Irving, a professor of virology at the University of Nottingham, said in a statement.

Adults are much more prone to suffer severe disease from hepatitis, and children are not usually affected, he said.

The public health investigation will likely focus on studying patient samples and trying to find potential toxins or viruses that might be responsible, Irving said.

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