You won't get any cases if the droplets just fall to the ground like rain. They have to float around for a while so people can breathe them in. That's why they have to be small, and the cropduster isn't designed for it.
A few modifications, though, and all bets are off.
Already outlined. It's better not to elaborate too much. It would be good to keep the antibiotics at hand to prevent any deaths, in case the wackjobs try anything at all. This should really scare no one, since the diseease is so suseptable to treatment at the first symptoms.