Following up your insightful post about fulminating pneumonia, the Busch family released his cause of death. He did, indeed, die from severe pneumonia that progressed to sepsis. Here's a link to the story:
https://www.foxnews.com/sports/nascar-kyle-busch-cause-death-revealed-family. I would post this in an FR category (Front Page News), but am not sure it would be allowed to stay there.