UK health officials are advising schools on how to combat Strep A infections after the deaths of at least 24 children since September.
The UK Health Security Agency (UKHSA) says the figures are higher this year compared with the previous two, likely as a result of withdrawing the measures implemented during the COVID pandemic.
What is Strep A - or GAS?
Strep A - or Group A streptococcus (GAS) - is a type of bacterium found in the throat and on the skin and in most people does not cause any symptoms - known as being "colonised", the NHS says.
However, it can cause a range of different illnesses of the nose, throat and lungs.
It can be spread through coughs, sneezes and skin-to-skin contact.
Those carrying the bacteria may have no symptoms, but are just as likely to pass on Strep A as those who have fallen ill.
Symptoms for Strep A include pain when swallowing, fever, swollen tonsils with white patches, swollen neck glands, a high temperature or a skin rash.
The bacteria can also cause any of the following:
skin infections like impetigo or erysipelas
Most cases of throat infection will get better on their own without treatment. Skin infections may require antibiotics.
However, GAS can also, on occasion, cause very severe infections - known as invasive GAS (iGAS).
What is iGAS?
Invasive GAS disease happens when the bacterium gets past the body's natural defences and enters parts of the body where it is not usually found, like through the blood, deep muscle or lungs.
The most severe forms of invasive GAS disease are Streptococcal Toxic Shock Syndrome - symptoms of which include high fever, low blood pressure, scarlet fever, kidney or liver damage and vomiting and diarrhoea - and Necrotising Fasciitis or "flesh-eating disease", which is an infection that destroys tissue and requires surgery. Both of these are rare, but Toxic Shock Syndrome has a high death rate.
Treatments include different types of antibiotics, and depending on how severe the symptoms are blood transfusions may be given.
What are the symptoms of iGAS?
Early signs and symptoms of invasive GAS include:
severe muscle aches
pain in one area of the body
redness at the site of a wound
vomiting or diarrhoea
How common is it in the UK?
iGAS disease is rare. There are between two and four cases per 100,000 people each year.
Ashish Joshi, Sky News health correspondent, said: "Parents need to be vigilant but not unduly concerned.
"While there is an uptick in cases, there haven't been many over the last few years because the COVID pandemic meant there were restrictions on people's movement."
He added: "It is a very common bug that children and adults can pick up, although the tragedies we are aware of tells there is a higher amount of more dangerous cases affecting children in a more dangerous way.
"But we mustn't be alarmed, and mustn't be saying all children will become ill and some may die.
"That said, it's important that parents, who will naturally be worried, should just be vigilant of the signs."
How dangerous is Strep A (GAS)?
It can be a serious illness, but if treated promptly with antibiotics, it is less of a threat. After at least 24 hours of antibiotics, it is generally thought to no longer be contagious.
Can adults get Strep A?
Adults can get Strep A, but it is more common for it to develop into scarlet fever in children.
Adults at increased risk for scarlet fever include parents of school-aged children and those who are often in contact with children.
According to the NHS, those at an increased risk of iGAS include those who are:
in close contact with someone that has Strep A
over the age of 65
use steroids or other drugs
have diabetes, heart disease or cancer
Which version of Strep A has caused the children to die?
A five-year-old girl in Belfast became the latest child to succumb to the infection, with deaths also reported in Hampshire, London, Buckinghamshire, Surrey and Penarth in Wales.
What should you do if you have symptoms?
Contact your GP and get medical advice straight away if you believe you or your child have symptoms of either GAS or iGAS.
Strep throat should be different from a regular sore throat, as the pain can come on quickly.
In response to the latest outbreak, a UK Health Security Agency (UKHSA) spokesman said: "As part of our public health response to last week's tragic news, we issued some general information about the signs and symptoms of scarlet fever, which is not uncommon, to schools in the vicinity of Ashford Primary.
"A number of other illnesses typically circulate at this time of year and parents, school and nursery staff are advised to be aware of the symptoms, to keep up with vaccinations and to seek advice from NHS 111 if they have concerns."