A further two cases of hepatitis in children have been confirmed in Scotland with the cause of the outbreak still unclear.
There are 13 children, aged between one and five, being treated in hospitals across Scotland for paediatric hepatitis.
Public health authorities said there were a number of potential causes under investigation but there was no link to the Covid-19 vaccine.
The UK Health Security Agency (UKHSA) said none of the 74 confirmed cases in the UK had been vaccinated.
However, coronavirus is being investigated as a possible cause along with a group of viruses called adenoviruses which may be causing the illnesses, as well as other infections or environmental causes.
Public Health Scotland said most cases have presented from March and that the hepatitis viruses commonly associated with the condition have been excluded.
Adenoviruses are a family of common viruses that usually cause a range of mild illnesses and most people recover without complications. They can cause a range of symptoms, including colds, vomiting and diarrhoea. While they don’t typically cause hepatitis, it is a known rare complication of the virus.
UKHSA said adenoviruses are commonly passed from person to person and by touching contaminated surfaces, as well as through the respiratory route.
The most effective way to minimise the spread of adenoviruses is to practice good hand and respiratory hygiene and supervise thorough handwashing in younger children.
Public Health Scotland said there is no clear connection between the cases, as yet, but that infection is considered to be a more probable source this time.
Dr Meera Chand, director of clinical and emerging infections at UKHSA, said: “We are working swiftly with the NHS and public health colleagues in Scotland, Wales and Northern Ireland to investigate a wide range of possible factors which may be causing children to be admitted to hospital with liver inflammation known as hepatitis.
“One of the possible causes that we are investigating is that this is linked to adenovirus infection. However, we are thoroughly investigating other potential causes.
“Normal hygiene measures such as good handwashing – including supervising children – and respiratory hygiene, help to reduce the spread of many of the infections that we are investigating.
“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.”
UKHSA, working with partners, will continue to make the public aware of findings throughout the course of the investigation.
Amid the outbreak medics and public health services have urged parents and carers to look out for signs of the condition that can be very serious.
While some types of hepatitis will pass without any serious problems, others can be long-lasting (chronic) and cause scarring of the liver (cirrhosis), loss of liver function and, in some cases, liver cancer.
The UKHSA is asking those looking after children to be vigilant for symptoms of jaundice, which can be a sign of liver inflammation.