Streptococci are a group of Gram-positive microbes that include infectious Group A streptococcus (Strep A) pathogens that can cause mild infections like a sore throat, more serious conditions like scarlet fever, and in some rare cases, sepsis or toxic shock. Now scientists have identified a novel strain of Strep A bacteria called M1UK, which the researchers think has led to an increase in the incidence of strep throat and scarlet fever since 2014. Although it is treatable with antibiotics, the researchers are stressing that other countries should investigate this microbe. The findings have been reported in The Lancet Infectious Diseases.
Invasive cases of Strep A are not only on the rise in the UK; the video above describes increasing cases in Canada.
"We've seen an unprecedented rise in the number of cases of scarlet fever since 2014 but it was only in 2016 there was a rise in the number of serious, invasive cases due to Strep A - which are thankfully very rare - coinciding with the seasonal rise in scarlet fever," explained the senior author of the study Professor Shiranee Sriskandan of the Department of Infectious Disease at Imperial College London. "Our research, done in collaboration with Public Health England, aimed to determine if there was a link between the increase in scarlet fever and the increase in invasive infections. In undertaking this research, we identified the new strain, linked to increases in both."
Scarlet fever often occurs in young children that have been infected by Strep A. The microbes release toxins that cause the symptoms and inflammation that is a hallmark of the illness. It’s most common from about March to May. The illness has surged in recent years in England; there were over 19,000 cases in 2016.
"Scarlet fever is a very visible signal of how much Strep A is circulating in the wider community and causing sore throats. Strains of Strep A that cause these commoner throat infections and scarlet fever are the same strains that cause rarer invasive diseases - and therefore a rise in these commoner throat infections including scarlet fever could lead to increases in all forms of Strep A infection," added Sriskandan.
Compared to the previous five years, confirmed cases of Strep A infections increased 1.5 times, around the same time that scarlet fever was spiking. Using many samples that had been collected and then stored at the Imperial College Infection Biobank, the scientists were able to analyze all kinds of Strep A infections. Many cases were caused by strains dubbed emm3 and emm4, while emm1 strain infections rose every year, causing five percent of cases in 2014, then nineteen in 2015 and 33 percent in 2016 - the main cause that year.
The researchers wanted to know whether the emm1 strain was changing, and they found a type within the emm1 group that carried 27 genetic mutations separating it from the rest of the group. This new strain can generate nine times as many toxins as other emm1 strains, which may explain the increased number of cases. After checking the patient data, the scientists found that all emm1 strains caused 77 percent of illnesses due to Strep A infections in spring 2016 in England and Wales.
Since this analysis only included strains that were in circulation until 2016, more work is needed.
"There is still uncertainty around the cause of the rise in scarlet fever - and whether it is a result of practice change, population or environmental factors," said the co-first author of the work, Dr. Elita Jauneikaite of Imperial."Research investigating the most appropriate way of reducing the burden of Strep A infections is currently underway - including work into developing a vaccine. We may also need to consider whether guidelines for diagnosing and treating throat infections may need to take evolution of new strains and complications like scarlet fever and invasive infections into account."