Experts remain unsure why the disease has surged in the United Kingdom. However, there are effective antibiotic treatments for the illness.

Is there a new British Invasion coming?

This time involving scarlet fever.

The bacterial disease has made a return in the United Kingdom.

The latest outbreak has stumped medical expertsand brought up the possibility that the illness could surge in the United States as well.

Scarlet fever is a bacterial infection caused by the Streptococcus bacteria that causes sore throat or “strep throat.”

It was once a deadly scourge during the pre-penicillin Victorian era.

This infection is characterized by not only the sore throat and fever but also a tell-tale red rash that is “sandpapery” and caused from toxins released by the bacteria.

In the U.K., the disease waned significantly from the early 1900s over the next century.

This was “largely due to improved hygiene, nutrition, living standards and healthcare,” according to the U.K.’s National Health Service.

In 2013, there were fewer than 10 cases of the disease per 100,000 people.

According to the most recent data published in The Lancet medical journal last week, the number of infections has now more than tripled.

In 2016, there were 33 cases per 100,000 people.

“England is experiencing an unprecedented rise in scarlet fever with the highest incidence for nearly 50 years,” the study authors concluded. “Reasons for this escalation are unclear and identifying these remains a public health priority.”

In the U.K., the scarlet fever cases mainly affected young children with the median age of infection at 4 years old.

For children under 10, there were 186 infections per 100,000 people, according to the report.

One in 40 children were admitted to the hospital, and serious complications appeared in less than 1 percent of all cases. No deaths were reported.

The study authors remain stumped by the spread of the disease.

They found that lab analysis didn’t point to a new kind of Streptococcus bacterial strain that might explain the new scarlet fever cases.

Although the disease has returned, the associated mortality rates haven’t.

Antibiotics remain an effective treatment for the disease.

As a result, mortality associated with the disease hasn’t reached the high levels of the past, according to an accompanying editorial.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center in Tennessee, said that scarlet fever was traditionally much more feared than simple strep throat.

“Scarlet fever had these overtones of much more serious infection,” he told Healthline. “Perhaps more likely for the bacteria to get into the blood stream and cause complications.

Exactly how many cases of scarlet fever appear in the United States every year isn’t immediately clear.

Schaffner says he doesn’t believe there’s been an increase like what was documented in the U.K.

In an emailed response, a spokeswoman for the U.S. Centers for Disease Control and Prevention (CDC) said that they don’t track noninvasive infections caused by group A Streptococcus bacteria.

These infections include common infections like strep throat and rarer ones like scarlet fever.

“We do estimate there are several million cases of non-invasive group A strep illnesses, like strep throat and impetigo [rash or sores around the mouth,] each year (but that data isn’t teased out),” the CDC said.

In the United States, Schaffner said, scarlet fever disease has been so rare that there have been generations of medical students who haven’t seen a case.

“Scarlet fever, like whooping cough, is a disease of yesteryear, and its return is indeed puzzling,” he said.

Schaffner explained that in the United States, incidences of scarlet fever began to wane in the 1960s.

“The thought was at the time that… many of those strains had mutated such that they lost the capacity to cause the rash,” he said. That “the genetic element was just lost.”

The new cases in the U.K. have coincided with a rise in Asia from 2009 to 2015.

However, the study authors said it wasn’t clear that these Asian outbreaks were related to the rise of the disease in the U.K.

Additionally, other cases weren’t present in the rest of Europe, which might be expected if it was linked to the Asian outbreaks.

Schaffner said that there is a potential for the disease to arrive in the United States, especially from children who travel from the U.K.

“A child could acquire group A strep and get on a plane and get off at Minneapolis and have contact with his or her cousins and spread the infection,” he said.

But parents shouldn’t be too concerned.

Schaffner pointed out that the scarlet fever infections appear to be effectively treated with antibiotics the way strep throat is treated.

When “we didn’t have penicillin, the group A strep was more likely to get into the blood stream and produce more complex illness,” he said. “Now it doesn’t get a chance to do that. We recognize it so quickly and treat it so promptly.”