G'day GUEST (?),
In my days as a specialist harmonica player, I always washed them ... even when they had wooden bodies that swell and cut your lips in long sessions. When plastic bodies became the norm, it was much easier to give them a good rinse in medium warm water - even rinse them under a hot tap (not too hot to hold, is safe for the harmonica). A few smart taps to shake out loose water, a quick run up and down the whole instrument, hole by hole, to get every note sounding, and I was back in business.
If I washed them often enough to stop build-up of crud from flattening the tuning ... there would be nothing to come loose in playing and no more infection risk than breathing what we laughingly call air, nowadays.