It runs in the genetics. It flares up with cold damp conditions. The cure is to remove all infected combs, change the queen out to new queen genetics, set hive where it gets sunlight, and give hive some ventilation.
There are differing degrees of chalk brood that I've seen in the past. One year it was pretty heavy in a couple of my hives. I don't mess around with it any more. I replace the queen and remove all infected combs, and make sure hive is not in a wet condition.
I've been keeping a few hives for the past 20-25 years, and no longer treatment free as I got tired of the losses.