Something else to consider.
Fomites are a means of transmission for Parvo.
Wonder if any of the outbreaks are nosocomial, cases picked up at the vet.
Especially with veterinary chains buying up so many practices, my bet is that to control costs, infection control gets short shrift.
I don’t believe it for a second. If word got out that a veterinary clinic was responsible for spreading parvo through unsanitary practices, it would be shut down in a heartbeat. I’m also sure that if a dog or other animal comes though the clinic with a diagnosis of parvo, the vet would order a thorough decontamination of the whole building and grounds outside.