My workplace has inside the bathrooms two options for cleaning one's hands, both sinks with soap and towels, and a dispenser for alcohol-based hand sanitizer. When opening the door to the bathroom one day, I found myself wondering if the presence of that hand-sanitizer on my hand was helping to protect me from the germs no doubt lurking on the handle from those who hadn't washed their hands, or had washed inadequately. Is there any effective protection from having hand-sanitizer on the hands when touching the handle?
Yes, to a degree. Since the stuff we touch will be on our hands and the stuff that's on our hands will be on what we touch. CDC:
Quickly reduces number of microbes, but not all
Less effective in greasy or dirty circumstances
So if the handle is greasy or visibly dirty the amount of microbes that are killed are decreased. It may be better to just grab handles with tissues.
Hand Sanitizer usually kills around 99% of common germs within 30 seconds
They can "kill" some viruses, but aren't slowed to make that claim by the FDA
I would take into factor that it dries fast. And that door handles can be pretty dirty. It also depends on the amount of sanitizer you use.