A new strain of group A streptococcus, which is able to produce significantly more toxin, is spreading in England and Wales, scientists say.
Strep A causes a range of infections, from a sore throat to scarlet fever.
The new strain’s emergence, reported in The Lancet Infectious Diseases, coincides with a rise in rare but potentially deadly invasive infections.
However, it does not explain the mysterious surge in scarlet fever cases during the past five years.
And there is no direct evidence the new strain causes more serious infection than other strains, experts say.
Scarlet fever is a very contagious infection that mostly affects young children.
The number of children with scarlet fever soared in 2014 and two years later there was an increase in cases of invasive