Anything in the Virus Chest is safe there. We usually suggest leaving items there for several weeks and rescanning it every few days as virus definitions are updated. You may find that it is a false positive (FP), in which case you can then restore it or delete it depending on the file.
You can also upload the file in the Chest to Avast for analysis to see if it is a FP, and this will be done on the next virus update…very soon.
Since you found a rootkit, I also suggest running a boot scan as well if you didn’t already.