UK strep A strain scarlet fever outbreak, New strain of Strep A that is NINE TIMES more aggressive.
An emergent and dominant strain of Streptococcus A is being blamed for the dramatic surge in scarlet fever cases in England and Wales from 2014 to 2016.
Britain’s National Health Service reported that scarlet fever cases reached a 50-year high in England in 2016, with 19,000 cases reported. In the years prior to 2014, the country averaged around 3 to 8 scarlet fever cases for every 100,000 people, but 2014 saw an increase to 27 cases per 100,000.
Approximately 15,000 cases of the bacterial infection were reported in England in 2014, and 17,000 were reported in 2015.
While investigating this spike in scarlet fever, Shiranee Sriskandan, MD, PhD, and colleagues at Imperial College London recently identified a new strain of Group A streptococcus bacteria — M1UK — that emerged as the dominant cause of Strep A infections in England and Wales during the scarlet fever surge.
As the team reported online in The Lancet Infectious Diseases, the emergent lineage of M1T1 Streptococcus pyogenes expanded quickly to become the largest single contributor to both non-invasive and invasive infections in 2016, characterized by dramatically increased production of the scarlet fever toxin, or streptococcal pyrogenic exotoxin A (SpeA).
“The findings raise the possibility that historical associations between epidemic waves of scarlet fever and invasive infections might also have been linked to strain pathogenicity, in addition to general population susceptibility,” the researchers wrote.
In a press statement, Sriskandan said that while the new bacterial strain appears to be largely limited to the U.K., genetic analysis of emm1 Strep A strains from around the world revealed single isolates of M1UK in Denmark and the U.S.
“The fact that we have identified two examples of it elsewhere suggests it has the potential to spread internationally and may already be present in other countries,” Sriskandan noted. “However, it’s also possible that the lineage will not last. In the past, some lineages have appeared and then disappeared quickly. Only further research on recent strains will provide more insights.”
To learn more about the Strep A strains causing the spike in illness in London and Wales, the investigators analyzed 135 non-invasive and 552 invasive emm1 genotype isolates collected from 2009 to 2016 and compared the samples with 2,800 global emm1 sequences.
The investigation revealed that the the Strep A strain types emm3 and emm4 were dominant during the initial phase of the scarlet fever surge in 2014. But in the spring of 2015 and again in 2016, emm1 emerged as the most dominant strain in cases of respiratory disease.
In northwest London, emm1 S pyogenes upper respiratory tract isolates increased during the March-to-May period, from 5% in 2014, to 19% in 2015, to 33% in 2016, the researchers reported.
Nationally, emm1 isolates increased from 31% of samples analyzed in 2015 to 42% in 2016.
“Sequences of emm1 isolates from 2009 to 2016 showed emergence of a new emm1 lineage (designated M1UK) — with overlap of pharyngitis, scarlet fever, and invasive M1UK trains — which could be genotypically distinguished from pandemic emm1 isolates by 27 single-nucleotide polymorphisms,” the team explained.
The M1UK isolates produced nine times more of the scarlet fever toxin SpeA than non-M1UK isolates.
Scarlet fever surges have not been limited to the U.K. China, South Korea, Vietnam, and Hong Kong have all reported a resurgence in the disease since the late 2000s.
Sriskandan and co-authors concluded that the M1UK lineage is distinct from emm1 sequences identified in Asia.
Writing in an accompanying commentary, Mark J. Walker, PhD, of the University of Queensland in Australia, and co-authors wrote that the analysis provides “further support that scarlet fever emm1 lineages from different geographical regions are evolving independently and are associated with different virulence characteristics.”
Walker and co-authors called for global surveillance systems to track group A streptococcus disease activity: “[This] report … sends out an important warning for the global public health community; recently emerging scarlet fever group A streptococcus strains have enhanced invasive potential, which might have profound implications for the future global health burden,” the commentators concluded.