I have Lancashire Heelers. There are always risks associated with attending any show or gathering where there are lots of other animals, but you need to take common sense precautions, make sure you own dog is fit and well before attending, keep away from close contact with other animals if you feel there is any chance that a dog is not well. It will soon be noticed by other exhibitors if there is any sort of problem.
Crufts is such a huge show with so many dogs that it is likely that there will be at least something there with either kennel cough or some sort of infection. You cannot spend your life worrying unnecessarily about something you know nothing about, but in the case of our breed show, we did know there was something to worry about, so it was cancelled to prevent any further spread.
What breed do you have - I am showing on the Friday and hoping to go back on the Sunday to do Discover Dogs and also go on the Vulnerable Breeds stand.