I grew up in Northern California and we frequently had temps of 100 or more and we started hunting on the opener on July 1st. We never had a problem with anything when it came to eating cottontails. I suppose other places may have. But since I left California, I've killed and eaten cottontails in New Mexico before the frost and here in Idaho before the frost. And in all three places we were told not to, and never had any problems at all.
As well, never known anyone to get sick. I have been told by everyone that said I would get sick they they all knew someone who ate a rabbit and it made them sick or killed them. But I'm thinking if that many people were effected there would be something on the news about it, or a big shortage of hunters.