Different lineages of group A streptococcus can gain and lose bacteriophages that encode pyrogenic toxins known as superantigens that have a profound impact on human T cell immune responses. The so-called erythrogenic toxins were first recognised to be associated with scarlet fever in the early part of the last century, a much-feared illness of children with high attendant mortality. However, in the latter part of the same century, when scarlet fever rates fell to an all time low, the same toxins came to be regarded more as the primary trigger of streptococcal toxic shock syndrome, a rare complication of invasive infection. Now, at a time where genuine concerns about antimicrobial resistance may discourage diagnosis and treatment of strep sore throat, we find ourselves again challenged with rising scarlet fever rates and hard-to-control seasonal outbreaks. The talk will examine how increased disease activity may be associated with emergence of novel toxigenic clones that demonstrate high transmissibility and can spread across borders.