When visiting relatives in Japan, I've used a public bath in a major hotel, a small one in Osaka, since my relatives there didn't even have their own bath. I also went to a public hot spring bath. My grandmother (on my Dad's side - not Japanese) went to Japan at 75 years old and was asked to take a public bath, which she was very leary of exposing herself naked in public (she is a very heavy set woman). Once she was finally talked into it, she loved it. Then in the next town they were visiting, she discovered the public bath and went off trotting to it, without a worry.

While unusual compared to America, where there is no such thing as a public bath - at least outside of ethnic neighborhood in large cities, I have no apprehension of using one, or fearing of getting diseased bathing in one.