Doorknobs are one of the filthiest surfaces in your home as far as bacteria are concerned. Don’t even get me started on public door knobs and pull handles. Just think: all sorts of people are using public locks and pull handles. Do you think all of them wash their hands after blowing their nose, picking up dog feces and going to the bathroom?
If you have to go through a public door, my advice is to avoid touching the door with your hand. Push doors open with your shoe or elbow. If there is a button for the disabled to open the door I push that button with my foot or knee or elbow.
An interesting development in the lock world is the invention of antimicrobial finishes. Here is an interesting article about them. The gist of it is that many lock manufacturers now offer their locks with an antimicrobial finish that inhibits growth of bacteria on the surface of the lock!
Obviously if somebody gets yogurt or cheese all over your doorknob the antimicrobial coating won’t be able to do much to help but if the hardware isn’t soiled, research shows that these coatings are effective. If you manage a public building, let me know if you want a quote for hardware featuring antimicrobial coatings. It may not require replacing your locks altogether, just the parts that people touch are coated and so that is the part that would be replaced.