How do we get reinfested with mites

This colony was treated in August with Mite Away Quick Strips. The hive had a low mite count after treatment. As fall progressed, the hive was reinfested with mites. The beekeeper treated with Oxalic Acid with a vaporizer. The pic from a week ago was after 2 days, now this pic from the same hive, is the mite drop after 9 days. You can see the mite drop produced hundreds of dead mites that are no longer parasitizing the bees and weakening the hive. Had she not treated, there is a good chance the bees would not have survived the rigors of winter,

A researcher recently was doing experiments on bee colonies. He had colored all the bees in the hive as part of his experiments. The hive had a very high mite count.
 The result was typical, all of a sudden all of the bees absconded. That is the scenario for fall, in a hive with a high mite count. One week the hive looks great and the next week all of the bees are gone.  Most beekeepers have experienced an empty hive if they have kept bees for several years. The question has been, where did the bees go?
 What the researcher found was the bees went to other colonies in a 1.5 kilometer area from the existing colony. He found colored bees in colonies near the hive that absconded. So all of the bees that were full of mites, went to other colonies and brought their mites with them. Now the neighbors colonies are threatened with high mite levels. Areas with many colonies in close proximity, such as Minneapolis, is a good bet for reinfestment of mites.
Now we know one way our  hives are getting reinfested with mites.