Was this breeder a private breeder? If so, are they NPIP certified? If you don't know, call them and ask. It's a program that inspects and certifies poultry breeders and hatcheries to insure serious poultry disease isn't spread around the country.
This certification should give you pretty good assurance the chicks they sell you will not be carrying disease. If they are not NPIP certified, you take a chance that you could be importing serious poultry diseases into your flock. Quarantine does nothing to safeguard your existing flock against these more serious viruses.
Here on BYC, I've directly participated in a thread where new chicks bought from a private breeder were carrying one of these contagious viruses (Marek's). All of the chicks died and contaminated the premises making it difficult for our original poster to have more chickens since this disease and many like it live a long time in the environment, sometimes years.
The OP called the authorities and they found some pretty serious violations, and the breeder was shut down. This tragedy could have been avoided by asking the simple question, "are you NPIP certified?"
This is even more important than quarantine. Call and ask. Meanwhile, take precautions such as hand washing and changing clothes when handling your existing chickens after handling this new chick.
