Imagine the sewage and stench that these 80k people produced with their minimal sanitation abilities. I know that the infant death rates must have been horrendous! these start-up civilizations, to which we owe a great debt, got their start in the areas that could benefit from organized agriculture, which is why the 3 centers were in China, Indus River and this 'Fertile Crescent'.
Woolley pointed out a cultural practice -- to bury the deceased family members under the (dirt/mortar) floor of the house -- which couldn't have been that hygienic, and he speculated that the large size of these cities may have been in part due to abandonment of contaminated homes. I doubt this though. And I don't remember reading that Gacy's family had to move out over that problem.