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A new, more toxic strain of Streptococcus A bacteria is causing an outbreak of scarlet fever in British children, researchers said.
The increase in scarlet fever is the largest observed since the 1960s. Between 2014 and 2016, the number of cases increased from 15,000 to more than 19,000. Infection tends to peak between March and May, according to the 'study.
"The new line [of strep A] seems to supplant its predecessor in the population, "said lead researcher Shiranee Sriskandan, professor of infectious diseases at Imperial College London.
This new strain also appears to produce more toxin than the previous strain, she said.
According to Dr. Marc Siegel, a professor of medicine at NYU Langone Medical Center in New York City, scarlet fever is easily treated with antibiotics, especially penicillin.
However, if streptococcal infections are not treated, they can spread throughout the body and become fatal, he said.
"There are in the United States every year 11,000 to 15,000 cases of invasive infections in children, which make up to 1,500 deaths," Siegel said.
He really expects this more aggressive strain of A streptococcus to manifest itself in the United States.
Sriskandan added that "this type of strain is totally susceptible to commonly used antibiotics, so resistance did not play a role in its emergence".
Streptococcus A causes infections other than scarlet fever, and some of them are also on the rise in the UK, Sriskandan said.
Streptococcal infection causes sore throat, fever, swollen lymph nodes and congestion. With scarlet fever, there is also a rash.
Siegel advises parents whose children may have streptococcus to consult their pediatrician and have them tested and treated with antibiotics if necessary.
For the study, Sriskandan and his colleagues examined the type of "emm gene" in Strep A that was responsible for scarlet fever.
Investigators found that the increase in scarlet fever in London in 2014 was related to the types of streptococcus A emm3 and emm4. In the spring of 2015 and 2016, however, throat infections were related to emm1 strains.
In 2014, only 5% of infections were registered, but in 2015, they had increased to 19% and in 2016 to 33%, the researchers discovered.
The emm1 strain has also become the dominant strain involved in other streptococcal A infections, with a 42% increase in streptococcal infections by 2016, according to the findings.
An analysis of the genetics of the emm1 strain revealed 27 mutations among the strains of 2015 and 2016, which increased the production of streptococcal pyrogen exotoxin toxin – responsible for scarlet fever infection and other infections.
This mutated strain, called M1UK, produces nine times more toxin than other emm1 strains, Sriskandan said. This is the strain found in 84% of all genomes tested in England and Wales, she noted.
The researchers then compared M1UK strains to 2,800 strains worldwide. Although M1UK is unique, strains from Denmark and the United States have also shown fragments of M1UK.
"The strains of streptococcus A that cause throat infections and scarlet fever are essentially the same as those that cause the rarest invasive infections – an increase in previous infections can lead to an increase in rarer infections," Sriskandan said.
A vaccine against streptococcal A would help a lot to prevent all these infections and would also reduce the conditions resulting from streptococcal infections, such as rheumatic heart disease, she added.
Dr. Marcelo Laufer is a specialist in infectious diseases at the Nicklaus Children's Hospital in Miami. He said: "The streptococcus does not change much, that's why it's still sensitive to penicillin."
What happens is that it attacks different bodily systems, so some diseases caused by strep throat are at the origin of strep throat spikes, so that others tend to evolve steadily.
"Strep has different mechanisms of disease, sometimes it invades, sometimes producing toxins and sometimes cheating the body for it to react, such as rheumatic fever," said Laufer.
It's the changing nature of the same bacteria that makes the task so difficult, he explained. "These are peaks and troughs of the same disease in different forms."
The report was published online Sept. 10 in The Lancet Infectious Diseases.
More information
To learn more about scarlet fever, visit the US Centers for Disease Control and Prevention.
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