May I suggest you consider why your harvesting honey in late September from a weak hive?
Secondary stress diseases (called secondary, because there are usually extenuating circumstances that allowed the disease to break out in the first place), are more seen in spring as bees are under stress in building up brood, dealing with cold snaps, balancing what needs to be fed with what needs to stay warm, and so on.
Genetics can always play into it. And I'm thinking if there ever was a time to requeen, it is when you see secondary diseases break out in odd times.
However, it is late in the season for requeening, etc. And I never suggest to combine a disease hive, even with minor chalk problem at this point of the year. Midsummer, I would suggest boosting the hive with some brood, perhaps requeening, etc.
For the record, weak hives should of been dealt with weeks ago in places with traditional winters.
I'd let them go and NOT increase the risk to any other hives at this time of the year. If they make it, they make it.