Texas is the only state in the U.S. that has attempted to track dog bites by breed. The Severe Attack Summaries were published from 1996 to 2002, then discontinued: the recorded information had never been complete [some counties didn’t report] and the Texas Department of Health believed the numbers were being misused and misinterpreted. (How do I know this? I phoned the Texas DSHS and asked.)
The CDC has verified that no other state has attempted to track dog bites by breed, and only one other state -- Minnesota -- has published a recent, state-wide study on dog bites.
Note the proviso in each of the Texas reports:
Note: the number of animals in various dog breeds in the overall canine population is unknown; therefore, no conclusions can be drawn concerning whether dogs of these breeds are prone to bite more often than other breeds or if these are merely the more popular breeds.