A shit you made me read it again too and they also say that

“I think the way to think about how global warming is putting selection pressure on microbes is to think about how many more really hot days we are experiencing,” said Casadevall of Johns Hopkins. “Each day at (100 degrees Fahrenheit, or 37.7 degrees Celsius) provides a selection event for all microbes affected — and the more days when high temperatures are experienced, the greater probability that some will adapt and survive.”

Idk, not a scientist. Seems like one of those complex chain reaction things, not a question of direct evidence for a single causing factor. Most of that stuff prefers warm temperatures and humid environments. Water from floods for example is full of delicious food for all kinds of organisms that can harm us. Also possible that the warming and seasonal weather extremes will speed up their evolution and make them generally stronger. Then combine that with the growing antibiotic resistance, and even weak and lame stuff like legionella will very soon be a greater danger.