More than 100 children have gone down with a mystery hepatitis condition with eight of them needing liver transplants.
The UK Health Security Agency (UKHSA) said a further 34 cases of the sudden liver inflammation have been identified, bringing the total across the UK to 108.
Cases have also been reported in the US, Ireland, Denmark, the Netherlands and Spain but scientists are still unsure what is causing them.
They suspect a virus and have not ruled out Covid-19.
However the prime suspect is are a family of common viruses called adenoviruses that usually cause a range of mild illnesses including colds, vomiting and diarrhoea. Most people recover without complications.
Some experts believe children’s weakened immune systems following repeat lockdowns could be a factor.
Dr Meera Chand, director of infections at UKHSA, said: “We are working with the NHS and public health colleagues in Scotland, Wales and Northern Ireland to swiftly investigate a wide range of possible factors which may be causing children to be admitted to hospital with liver inflammation known as hepatitis.
“Information gathered through our investigations increasingly suggests that this is linked to adenovirus infection. However, we are thoroughly investigating other potential causes.
“Normal hygiene measures such as thorough handwashing (including supervising children) and good thorough respiratory hygiene, help to reduce the spread of many common infections, including adenovirus. We are also calling on parents and guardians, to be alert to the signs of hepatitis (including jaundice) and to contact a healthcare professional if they are concerned.”
Hepatitis symptoms include dark urine, grey-coloured poo, itchy skin, jaundice, high temperature, vomiting, loss of appetite, muscle and joint pain.
It is usually caused by viruses hepatitis A to E but in these cases the children were found not to have had any so the cause is still unknown.
Dr Kimberly Marsh, an epidemiologist at Public Health Scotland, wrote in the journal Eurosurveillance that children could be “immunologically naive” to the virus because of pandemic restrictions.
She said: “The leading hypotheses centre around adenovirus — either a new variant with a distinct clinical syndrome or a routinely circulating variant that is more severely impacting younger children who are immunologically naive.
“The latter scenario may be the result of restricted social mixing during the pandemic.”
The UKHSA said Covid-19 vaccines were not causing the cases as non of the children had had a jab.
So far 79 of the affected youngsters are in England, 14 are in Scotland and the remainder are in Wales and Northern Ireland.
All the children affected presented to health services between January 2022 and 12 April 2022.
