All the proper hygiene in the world won't prevent you from being infected if there's an overnight explosion in cases while you're in contact with hundreds of people in airports, airplanes and social gatherings.

Even if you did manage to avoid getting sick, there's a chance you could get stuck in quarantine in Japan, the US or both as countries become more aware of the virus' dormancy.

Anecdotally, I have several friends who have cancelled non-refundable trips. If it were me, the desire to go on the trip wouldn't outweigh the stress of worrying about being infected, being held in quarantine, or traveling while a global panic sets in.