Parents are being advised to be on the lookout for signs of scarlet fever, a highly contagious bacterial illness that’s seen a sharp rise in recent years.

Experts have been baffled by the increase in cases of scarlet fever, which suddenly spiked in 2014 and has continued to climb since. Although usually mild and treatable with antibiotics, scarlet fever - also known as scarlatina - can lead to complications such as pneumonia.

Public Health England has issued the warning as the illness reaches a 50-year high in the UK, particularly in parts of Kent, Devon, the East Midlands, Yorkshire, the Humber and Swansea. Between 2013 and 2014, cases more than tripled from 4,700 to 15,637, with no obvious explanation as to why. 17,000 cases were reported in 2016, while the latest Health Protection Report showed that 6,225 cases of scarlet fever had been reported since mid-September 2017, compared to 3,764 for the same period last season.

Scarlet fever mainly affects children and tends to be seasonal. Symptoms include a sore throat, headache, fever and a distinct pinkish-red rash, characterised by a sandpaper feel. There’s no vaccine against it, unlike measles, with the infection caused by a bacteria that releases a toxin, resulting in the rash and a red tongue. Scarlet fever spreads when an infected person coughs or sneezes, so anyone diagnosed is advised to stay at home for at least 24 hours after the course of antibiotics has begun.

PHE director Nick Phin said: “It’s not uncommon to see a rise in cases of scarlet fever at this time of year. Whilst there has been a notable increase in scarlet fever cases when compared to last season, greater awareness and improved reporting practices may have contributed to this increase.

“Scarlet fever is not usually a serious illness and can be treated with antibiotics to reduce the risk of complications and spread to others. We are monitoring the situation closely and remind parents to be aware of the symptoms of scarlet fever and to contact their GP for assessment if they think their child might have it.”

Parents are advised to see the GP or call the NHS helpline if you think you or your child are showing signs of scarlet fever, or you’re being treated for scarlet fever but the symptoms haven't improved after a week or are getting worse. The illness is often diagnosed simply by the GP examining the rash, or sometimes using a cotton bud to take saliva from the throat for testing.