Talk about a massive over reaction, reformat.
Whilst there is no doubt this was a huge pain in the rear, no way it should have required a reformat to resolve. Even if you deleted all the files detected (never a good option without full investigation) it wouldn't have touched the system files (certainly none reported in the topics I viewed).
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.
Restore a false positive from avast chest (version avast 4.
, see
http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=376.