Parents are urged to look out for symptoms of scarlet fever as cases hit an almost 50-year high.
At the moment, Yorkshire and the Humber is being badly hit, as is London and the East and West Midlands.
Some 600 cases a week are being diagnosed across England following a steep rise in infections recently.
PHE expects a further rise in the next few weeks as the peak season for the fever occurs, usually between late March and mid April.
What are the symptoms?
Early signs to look out for are
- a sore throat
- 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.
What should you do?
The infection needs prompt treatment with antibiotics owing to the potential for complications and more severe illness caused by its group A strep bacteria.
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."
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.
How is it spread?
Scarlet fever is spread through close contact with infected people or indirect contact with objects and surfaces contaminated with the bacteria.
How long does it last and serious is it?
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.
PHE said tests have ruled out the possibility of a newly emerging strain of strep group A that is more easily spread between people.
Is there a vaccine?
How big is the recent increase in cases?
There have been 6,157 reported 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 steeply in 2014 and, in 2015, there were 17,586 cases.
In Yorkshire, from 2010/11 to 2014/15, there were an average of 65 annual cases, however the 2015/16 figure is 121. This represents an increase of 86 per cent on the five-year average. There are now 2.3 cases per 100,000 people in the region, compared to an average of 1.2 over the past five years.
Where I can find out more imformation?