I actually saw someone wearing a mask on the way to work today. Like I said, it is very common in Asia, and with the swine flu outbreak not losing any momentum, I expect to see more mask wearers on BART in the Bay Area. Apparently there are different grades of masks, and not all protect the wearer from bacteria and viruses. My parents, being the big worriers that they are, sent me a case of N95 masks. Check the CDC website for a list of certified swine flu protection masks.
Am I going to wear a mask on BART? Probably not!! But I will place one in my bag just in case I encounter someone who has all the symptoms. Meanwhile, I will continue to use drench my hands and arms in Purell after each ride.