Why is this a mystery? Besides the obvious sanitation and living condition differences, the folks that lived through had a genetic reason for living through it. Those that died genetically are much less represented today than they were back then.
Agreed. I’m not a scientist but I’m surprised that things like hygiene and exposure to many conditions unknown to most people today are not being considered. The diets back then were inferior in quality to today’s, leading to a less than stellar immune system to begin with. Couple that with constant exposure to feces, fleas, and every other contagion out there.... it’s probably a wonder more did not die! This disease was carried by a specific flea — feeding on specific rats...Given the lack of hygiene and regular exposure to rats and fleas for most people...not really a mystery that the disease, once contracted, would spread as rapidly as it did.