"Whilst current rates (in England) are nowhere near those seen in the early 1900s, the magnitude of the recent upsurge is greater than any documented in the last century," said study author Theresa Lamagni of Public Health England, the agency that funded the analysis. "Whilst notifications so far for 2017 suggest a slight decrease in numbers, we continue to monitor the situation carefully ... and research continues to further investigate the rise."
Identified by a bright red rash that looks and feels like sandpaper, scarlet fever is a highly contagious disease caused by the same bacteria behind strep throat, group A Streptococcus pyogenes.
Historically a common cause of childhood death, scarlet fever had been declining over the past two centuries, according to the study, with any rise in cases typically following a "natural cyclical pattern" every four to six years.
But since 2009, cases have been steadily increasing in several East Asian countries, including Vietnam, South Korea, Hong Kong and mainland China.
An outbreak then hit England, where cases tripled in one year, from 4,700 in 2013 to 15,637 in 2014. Infections continued to rise to nearly 20,000 in 2016, a 50-year high for the United Kingdom, according to the analysis.
Hospital admissions during the outbreak in England are also high, the researchers said, nearly doubling between 2013 (703 cases) and 2016 (1,300 cases).
Identifying scarlet fever
Although anyone who gets strep throat can get scarlet fever, also known as scarlatina, the disease typically strikes children under the age of 10. Frequently spread by droplets via coughing and sneezing, group A strep can also hide on doorknobs, plates and utensils for hours
The red rash that gives scarlet fever its name typically starts on the neck and face and spreads to the chest, the back and other parts of the body. At first, the rash will look like a bad sunburn, but then it will begin to raise and become bumpy. If pressed, the red skin will turn white; it can also be itchy. Once the rash subsides, the skin will often peel, especially on the groin, fingertips and toes.
A very sore, red throat that makes it difficult to swallow, along with a fever of 101 or higher, is a key sign of scarlet fever, along with swollen neck glands, headaches and body chills, nausea and vomiting.
An early symptom can be a "strawberry" tongue -- one that looks more red and bumpy than usual -- along with a whitish coating on inside of the throat. Other telltale signs include be a flushed face (except for a white streak around the mouth) and red streaks in the creases of the skin, with the armpits, knees and elbows showing a deeper hue.
Treatment for scarlet fever is the same as for strep: a course of antibiotics, which must be completed to be rid of the bacteria and avoid a relapse. If the regimen is followed appropriately, the disease is usually gone within a couple of weeks. Left untreated, it can lead to serious illness or even death.
Complications of scarlet fever can include Bright's disease, a form of kidney damage, and rheumatic fever, an autoimmune disease that affects the heart, joins, skin and brain. If rheumatic fever affects the heart, it can cause long-term damage. That's one of the reasons scarlet fever was a leading cause of heart disease for adults before penicillin was discovered.
Over the centuries, scarlet fever has caused devastating epidemics
. Those infected were often isolated for weeks, while their bedding and belongings were burned to prevent disease spread. Why the prevalence of the disease began to decline, even before the wide-spread use of antibiotics, is a mystery.
Detective work is underway
Why the disease is making a resurgence today is also a mystery, according to the study. Investigators are looking at such possibilities as a change in human immune status, environmental causes and even the disease traveling from Asia to England, although evidence for that is slight. Though the cases in the United Kingdom came from at least three known strains, only one of those was also seen in Hong Kong, and only in few cases.
"Whilst there is no clear connection between the situation in the UK and East Asia, a link cannot be excluded without better understanding of the drivers behind these changes," Lamagni said. "The hunt for further explanations for the rise in scarlet fever goes on."
Meanwhile, she suggests that parents in England keep an eye out for telltale signs and act quickly to get their children, or themselves, to a doctor for evaluation and treatment.
"Guidance on management of outbreaks in schools and nurseries has just been updated, and research continues to further investigate the rise," she said. "We encourage parents to be aware of the symptoms of scarlet fever and to contact their (general practitioner) if they think their child might have it."
In a comment published alongside the paper, University of Queensland professors Mark Walker and Stephan Brouwer recommend that public health systems around the world be on guard.
"Scarlet fever epidemics have yet to abate in the UK and northeast Asia," they wrote. "Thus, heightened global surveillance for the dissemination of scarlet fever is warranted."