What is the infected file name, where was it found e.g. (C:\windows\system32\infected-file-name.xxx) ?
Check the avast! Log Viewer (right click the avast 'a' icon), Warning section, this contains information on all avast detections.
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.
If it keeps coming back, there is likely to be an undetected or hidden element to the infection that restores or downloads the file again.
What is your firewall ?
If you haven't already got this software (freeware), download, install, update and run it, preferably in safe mode and report the findings (it should product a log file).
SUPERantispyware On-Demand only in free version. MalwareBytes Anti-Malware freeware version
http://www.softpedia.com/get/Antivirus/Malwarebytes-Anti-Malware.shtml.