Frozen tail shrimp?

I don't see why it would make any difference, but you're probably better off buying raw shrimp and boiling it yourself. This will significantly reduce the amount of bacteria in it. But if you decide to go with the pre-cooked stuff, you might want to at least run some hot water over it then chill it in the refrigerator. Again, this will kill any residual bacteria that has built up since it was stored.