I recently just started getting the blurry issue. The 'work around' as others have said is entering the config menu for a second. But, I would like to add some extra info to this issue. (Which I DO think is some type of bug) This issue will happen immediately after a respawn on the first zombie hit. I do not think this is a blood issue as others have stated.

This has only recently started to happen AFTER I upped my game resolution to my native 1920x1080 screen resolution. Previously I was using something around 1280x960(can't remember exact #). I reduced the resolution back to the previous (default?) setting under Config->Video->User Interface, and the problem is completely gone. Maybe others have had a similar experience with changing video settings?