I pretty much follow a couple or rules I set for myself when I first started travelling very frequently a long time ago...
1. If a person is hacking and coughing in the plane immediately behind me or adjacent to me, I try and move seats. If I can't move, I try and face away from them for the duration of the flight - this is where window seats are particularity handy.
2. I clean down surfaces that are going to touch my mouth, polish cutlery, wipe clean the tops of cans or bottles, always check glasses to be clean and take great care when getting juice at the QP that I push the lever with my finger to fill my glass rather than using my glass - how many QP members have you seen stand at the juice dispensers, knock back a glass then refill?
3. I never touch hand rails - stationary or moving unless I totally can't avoid it.
4. I always wash my hands after using the toilet, then paper towel the door to get out. I don't care about seeing paper towels piling up behind the door, I figure that the number of times I use the toilet at airports is so infrequent, and every time I do use the toilet, I see paper towels piling up behind the door, the problem is not mine that there is no waste paper basket there, its airport managements!
5. I avoid food stored in glass cabinets without a closed door on the back
6. I avoid purchasing food where the food is prepared by the same person who accepts your money!
7. With the advent of hand sanitiser, I carry a bottle with me all the time, and I use it before meals or any activity where my hands may come in contact with anything I am going to eat. I have also started wiping the tops of cans with a tissue with a smear of sanitiser on it - every time I do, there is gunk coming off the can brim! (I don't use plastic cups to drink from)
I have avoided (touch wood) a serious flu or cold for many years now and I hope these simple actions I take help in the process of avoiding them.
Or it could be the alcohol in my system doesn't allow them to survive
Mr!