Streptococcus group-A is a gram-positive extracellular bacteria. Group-A is strep includes type-M (em), which is more virulent, and has more than 80 serovars. Strep type-M adheres to epithelium and invades epithelial cells intracellularly; and can induce molecular mimicry and cytokine storms, from an immune response to M-proteins and cell debris, after the acute infection appears to have resolved. Acute intracellular viral infections can act synergistically with other intracellular pathogens, to worsen acute illness.
Approximately 30 % of children are positive for strep, without symptoms; and approximately 30% of children with strep can develop Kawasaki’s disease. Approximately 30% of tonsils removed at surgery had intracellular strep. Many diseases are known to be caused by, or are “associated” with, streptococcus, including: Rheumatic fever and scarlet fever (heart); Henoch-Schonlein Purpura, now known as IgA vasculitis, and a/k/a post-streptococcal glomerulonephritis (kidney); Bechet’s syndrome and Chilbains (skin); Kawasaki’s disease (autoimmune); and sepsis, toxic shock and multi-organ failure.
Post covid multi-system inflammatory syndrome (PMIS), a/k/a multisystem inflammatory syndrome in children (MIS-C), is a description of symptoms and findings. Different specialties have described MIS-C as similar to all of the above named diseases. Perhaps these diseases have a common root infectious origin (or more than one infectious origin); and in MIS-C the underlying pathogens erupt to increase the severity of acute viral illness. We cannot know until MIS-C children are tested for underlying pathogens, in addition to covid-19.