Last year a breeder brought her dogs who had kennel cough to a very popular conformation trial in our area. One of the competitors said to her "it sounds like your dog has kennel cough." She replied, "Yes, but they don't refund my money for Kennel cough, so we're competing!". An incredible amount of dogs became sick after that weekend, and because our dog community is small, it spread through the other dogsports over the course of the next few months well.
3 months later, my friend had to pull her dog out of an agility trial because of kennel cough (her dog's breeder had been at the conformation show - it went through her dogs, and despite taking precautions was eventually passed on to Maverick as well). Unfortunately, the agility trial here doesn't refund money if your dog has kennel cough - thank goodness she had the common sense to pull her dog out of the trial, unlike the lady at the conformation trial.