People don’t like discussing shit, but it has to be done. Decades ago, I read an article on this very subject, and still new bathrooms in stores and public buildings are built wrong in almost every way, almost guaranteeing that anyone leaving one will have fecal matter on his hands.
The best design has no doors at all. Without doors, the rest of the design problems are fairly easy to solve. Costco has one of the best implementations, eliminating doors at the entrance to the bathroom, but still each individual stall has a door and a lock. The latter should be able to be automated by purely mechanical means, simply by having a slightly elevated floor, which when stepped on, closes and locks the door. Perhaps an X prize could be established for the engineer who comes up with this or another innovative solution.
A doorless design takes a lot of space, though, so I can understand why smaller retail spaces cannot afford it. The next best thing is self-closing doors that open from the inside, meaning one can simply lean against the door, or push it open with a foot, to exit the bathroom. Let’s assume that people entering the restroom are less likely to have fecal microbes on their skin, and focus our primary attention on what we can do inside the restroom to minimize risk, although the entry problem could be solved using the same electrical door activators that are used for ADA compliance. For that matter, the same could be used for exiting, but as electrical solutions are prone to multiple modes of failure, I will de-emphasize such suggestions.
Next down the list would be lever-style door openers rather than knobs, at least on the inside of the door. This at least allows one to open it with an arm or elbow rather than the fingers. In last place, where we find most bathroom installations, are the doors with simple knobs and locks that must be touched with filthy fingers. One way to minimize the danger with these is to have a paper towel dispenser, with a well-maintained supply, close to the door, and a suitable disposal bin nearby, either inside or outside the restroom. This way, those exiting can grab a towel, and touch the door handle indirectly using it, throwing it away immediately afterwards. Hand sanitizers may also be made available, but these have their own problems.
After the doors, or elimination thereof, washing and drying hands is of major importance, particularly while western-style use of toilet paper, rather than the more civilized bidet, remains in vogue. I’ve noticed in recent years (perhaps since Liebeck was scalded by coffee) that most if not all Starbucks restrooms have no hot water; the best one can hope for is tepid, but often it’s simply cold. For drying, paper towels, while their environmental impact may be problematic, are arguably far better for sanitation than hot air dryers.
This article is far from complete. I will update as time permits.