The last six months have delivered unprecedented rates of group A streptococcal infection across Europe, with unusual clinical presentations, sometimes reminiscent of reports from 100 years ago. Notably younger children were impacted by increased rates of scarlet fever, invasive infection, typically including empyema and other suppurative complications, as well deaths that led to intense public concern. What led to the upsurge and could we have predicted it? Was it increased strain virulence, increased population susceptibility, or co-circulating respiratory viruses?
A number of previous increases in group A streptococcal population activity can be traced back to evolutionary changes in pathogen genome content, pointing to a key role for the pathogen. What then, should be done to reduce the impact of a pathogen that is able to change and rapidly expand in the human population, but only very rarely causes invasive infection? Public health campaigns to increase awareness can have unforeseen consequences. While some public health interventions can potentially interrupt pathogen transmission, what else should we do to reduce the impact of group A streptococcus, and can we control pathogen change?