I started obsessive watching the info coming out of Europe, particularly Italy, in maybe mid-February. That month I flew through Texas for a conference, and overheard people commenting about concern with international travel.
When I got back, I sat in on some interviews; someone joked about hand shaking since I'd recently flown, and I realized they were right, although they didn't mean it. I stopped shaking hands.
The next week I didn't shake my doctor's hand. She was initially surprised, then agreed it made sense.