The fact is that there are numerous reasons for soft shelled eggs and eggs dropped off roosts that are not due to actual disease. There are no waterfowl around here anywhere, wild birds do not reside in my coops, though once awhile back, a wren must have flown in through the pop door just as we were locking up and no one noticed until morning when she was frantically trying to get out, the one and only time a bird has been inside any of my coops for any length of time.
Many hens have egg issues during hard molts. Some have them due to age. Some eat plenty of calcium but do not absorb it for some reason that can have to do with vitamin D or other deficiency in their bodies. So, many, many reasons for soft shelled eggs.