I consider a 1 week quarantine barely scratching the surface, I quarantine fish at least 3 months before adding to the main tank.
many diseases take at least that long to become evident.
A friend who runs a public aquarium, Q.T.s for 6 months.
That said, I barely ever use feeder fish, and consider using them an epidemic waiting to happen, and as a former microbiologist, I find the random use of antibiotics the perfect way to produces resistant bacteria, and create another plague waiting to happen.
Might not be today, or in 3 months, but the likelihood (to me) is not worth the risk.