“ In the 20th century, scarlet fever was the leading cause of death in children, with a mortality rate of 20%.” Do you mean the 19th century when you talk about the late 1800’s as the 20th century? My brother had scarlet fever twice in the late 1950’s and he is now 82.
I was quoting.
The quote probably refers to circa 1900.
I should have read it more carefully and searched for and used another quote.
My apologies.