that's the nice thing about a new hive, swarm or package
. the brood break reduces the numbers, and as robo said, the packages have usually been treated.
when you do find mites, don't panic. you are going to have them. the key is to monitor mite load and have a plan for that time when your mite load is unacceptable. every board i pulled had a few mites on it. 1/2 a dozen or so. the one that got me worried, had many. that hive got treated with apiguard.