When eggs are laid they have a protective coating, called the "bloom", from the hen's reproductive tract. This bloom acts as a barrier between the eggshell (which is porous) and the outside world. It prevents bacteria from getting into the pores of the shell and infecting the developing chick.
Feces on the egg are an aesthetic issue, not a hygiene issue. I would use a DRY paper towel at MOST (sandpaper, for example, will remove the bloom and damage the shell), but personally I would leave it alone.