Parents are being urged to look out for symptoms of scarlet fever as cases hit an almost 50-year high.
Some 600 cases a week are being diagnosed across England following a steep rise in infections recently, with 6,157 cases from September 2015 to now, Public Health England (PHE) said.
In 2010/11, there were just 1,457 infections diagnosed over the same period, jumping to 5,010 in 2014/15.
In England and Wales in 1969 there were 16,093 cases in total followed by a long dip. Cases began to rise dramatically in 2014 and, in 2015, there were 17,586 cases.
PHE expects a further rise in cases in the next few weeks as the peak season for the fever occurs, usually between late March and mid April.
At the moment, Yorkshire and the Humber is being badly hit, as is London and the East and West Midlands.
The infection needs prompt treatment with antibiotics owing to the potential for complications and more severe illness caused by its group A strep bacteria.
Early signs to look out for are a sore throat, headache and fever with a pinkish/red sandpapery rash appearing within a day or two.
The rash usually first appears on the chest and stomach before spreading to other parts of the body. Scarlet fever is highly contagious and children aged two to eight are most at risk.
Dr Theresa Lamagni, PHE's head of streptococcal infection surveillance, said: "Individuals who think they or their child may have scarlet fever should seek advice from their GP without delay as prompt antibiotic treatment is needed.
"Parents can play a key role in recognising when their child needs to be seen by their GP."
Scarlet fever is spread through close contact with infected people or indirect contact with objects and surfaces contaminated with the bacteria.
Symptoms of scarlet fever usually clear up in a week and most cases are uncomplicated as long as children finish the course of antibiotics.
Potential complications include ear infection, throat abscess and pneumonia. PHE said the parents of any child who does not show signs of improvement within a few days of starting treatment should seek urgent medical advice.
Long-term health problems from scarlet fever may include rheumatic fever, kidney disease or arthritis.
Any child diagnosed with scarlet fever should not go to school until at least 24 hours after the start of antibiotic treatment while any adult affected should stay off work for at least 24 hours after starting treatment.
There is currently no vaccine for scarlet fever.
PHE said tests have ruled out the possibility of a newly emerging strain of strep group A that is more easily spread between people.