Microbially, the best public restrooms are in hospitals. If you want the cleanest, pull in to the emergency room. Next are your fast-food restaurants, and the worst are airports and bus stations. The more stalls the better, by the way. And the first stall is the safest, because fewer people use it.
Toilets have an aerosol effect that remains widely unrecognized.
One way to see this is to put a dye in the toilet, flush it, and then hold a piece of paper over it. Refrigerators in the laboratories held hundreds of brightly colored translucent petri dishes in which cell cultures were growing. Some were from Gerba's own experiments. For the most part bacteria are easily identified by local officials, but many viruses and parasites can be both hard to detect and hard to eliminate. Gerba pointed to a plastic bag on top, containing underwear to be washed.