The notion that a world-wide flood would destroy all diseases is absurd. And the notion that the things that cause diseases in the first place would never occur again, is even sillier.
Diseases are caused by things like genetic or developmental errors, infection, poisons, nutritional deficiency or imbalance, toxicity, or unfavorable environmental factors.
So, does T.O. really beleive the flood would have prevented any of that to ever happen again ?