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Deletion isn’t really a good first option (you have none left), ‘first do no harm’ don’t delete, send virus to the chest and investigate.

There is no rush to delete anything from the chest, a protected area where it can do no harm. Anything that you send to the chest you should leave there for a few weeks. If after that time you have suffered no adverse effects from moving these to the chest, scan them again (inside the chest) and if they are still detected as viruses, delete them.

If you can give an example of some of the infected files:
What is the malware name, the infected file name and where was it found e.g. (malware name, C:\windows\system32\infected-file-name.xxx) ? Check the avast! Log Viewer (right click the avast icon), Warning section, this contains information on all avast detections.