Life-threatening Strep A infections are four times higher now than they were before the Covid pandemic, health authorities have warned.
The bacteria has killed six primary school age children in Britain in the last month, five in England and one in Wales.
The bacteria normally causes tonsillitis, also known as strep throat, or scarlet fever, but in severe cases can manifest as a more severe form of disease called invasive Group A Strep (iGAS).
This occurs when the microbe moves beyond the normal realms of infection, such as the respiratory tract, and reaches the blood, for example, where it can lead to sepsis or shock and, in extreme cases, meningitis.
Data from the UK Health Security Agency (UKHSA) shows that in pre-pandemic times for children aged between one and four years old there were 0.5 cases of iGAS per 100,000 people. However, the current figure is 2.3 per 100,000, a fourfold increase.
For children aged between five and nine years old it has increased by more than a factor of three, up from 0.3 per 100,000 to 1.1 per 100,000.
Cases of scarlet fever, which is a different disease but caused by the same bacteria, have also been increasing in recent months.
Official data shows that in the most recent week there were 851 cases of scarlet fever, more than four and a half times the average number of cases (186) as in the same week in pre-pandemic times.
A senior health expert in the Government also told The Telegraph: “Now that everything's going back to normal we are going to see these cases coming back just like we did before the pandemic.
“There may be a few more cases now than there would have been before [Covid] because all these kids didn't get any infection during the pandemic and therefore there are more kids around who haven’t had it.
“If this had been spread over three years it may not be as high at all but because they're all getting it together it looks like there's a lot more infections.”
A primary-age pupil from St John's School, Green Man Gardens in Ealing sadly died of invasive Group A Strep (iGAS) this week and it comes as health officials confirm to the Telegraph that a young boy from high Wycombe also died of iGAS last month.
A young girl in Wales and a child in Surrey also died from the bacterial infection within the last week. The known tally of deaths from Strep A cases is now five.
There is an outbreak of the disease in the Surrey school of the first case with powerful antibiotics given out widely to get it under control.
But the situations in Ealing, High Wycombe and Penarth are thought to be isolated cases and not school-based outbreaks.
Health authorities issued guidance recently saying that children who recently had flu or chickenpox are more likely to develop a serious case, such as iGAS, if they catch Strep A.
This can happen as a weakened immune system or an open sore can accelerate the progress of the bacteria into the body.
Chickenpox causes lesions which allows the bacteria to get into the bloodstream and this makes it easier for the invasive form of the disease to occur.
For flu, the viral infection damages the respiratory system and changes the immune system, which makes it easier for the bacteria to spread into deeper areas where it can cause more harm.
Official statistics from the UK Health Security Agency (UKHSA) show that for every 100,000 cases of scarlet fever, 3.1 people will develop iGAS.
There are concerns among experts that lockdown measures enforced during the pandemic stopped the circulation of other seasonal diseases and that now the pathogens are circulating at much higher levels.
For the last two winters there have been very few seasonal viruses circulating, with social isolation measures enforced as a result of the Covid pandemic ensuring other infectious diseases did not spread.
“It also may be that with lots of respiratory viruses around (as expected at this time of year), having [Strep A] circulating as well results in more invasive disease (mucosal damage from viral infection allows entry) but we don't have numbers to confirm that yet,” Dr Whittaker told The Telegraph.
“As always, if parents are worried then they should seek medical attention.”