At least 30 children have now died in the UK from invasive Strep A disease (iGas), new figures show.
Some 25 under-18s have died in England from the infection so far this season, dating between September 19 and December 25, the UK Health Security Agency (UKHSA) said.
Two under-10s in Scotland have died with iGas since October 3, Public Health Scotland announced on Wednesday.
And the deaths of three children from iGas in Belfast and Wales have also been recorded by the UKHSA, bringing the number of child deaths in the UK to 30.
The agency’s data has recorded 151 cases of iGAS in children aged one to four this season, compared to 194 cases in that age group across the whole year of the last comparably high season in 2017 to 2018.
There have been 102 cases in children aged five to nine, compared to 117 across 2017 to 2018.
Across all age groups in England, there have been 122 deaths from iGAS.
In the 2017 to 2018 season, there were 355 deaths in total across the season, including 27 deaths in children.
The UKHSA said iGas infections remain rare and the majority of cases continue to be in the over-45s.
It said the data shows an “out-of-season increase” in Strep A and scarlet fever infections and a higher number of cases of both diseases than seen in a typical year.
There have been 33,836 notifications of scarlet fever this season, compared to 4,672 at the same point in 2017 to 2018.
Dr Obaghe Edeghere, UKHSA incident director, said: “We are continuing to see a rise in scarlet fever and ‘strep throat’ and this is understandably concerning for parents.
“However I would stress that the condition can be easily treated with antibiotics and it is very rare that a child will go on to become more seriously ill.
“Over the winter, there are lots of illnesses circulating that can make children unwell and so it is important to avoid contact with other people if you are feeling unwell, wash your hands regularly and thoroughly and catch coughs and sneezes in a tissue.
“I would also urge all those eligible for free winter vaccines to take advantage of these.
“Most winter illnesses can be managed at home and nhs.uk has information to help parents look after children with mild illness.
“However please do make sure you speak to a healthcare professional if you believe your child is getting worse, for instance (if) they are feeding or eating less than normal, are dehydrated, has a high temperature that won’t go down, is very hot and sweaty or seems more tired or irritable than normal.”
Group A strep bacteria can cause many different infections, ranging from minor illnesses to deadly diseases.
Illnesses caused by Strep A include the skin infection impetigo, scarlet fever and strep throat.
While the vast majority of infections are relatively mild, sometimes the bacteria cause a life-threatening illness called invasive group A Streptococcal (iGAS) disease.