One thing I was told - if you are immuno suppressed at all, try and avoid putting your hands directly on the supermarket trolley handle. Wear gloves, or use a wipe on the handle. Just watch people cough and sneeze into their hands and then put their hands on the trolley handle ..... it grosses me out.
Also the door handle out of the loo in the supermarket - all those total oiks who don't wash their hands touch that handle .... (also the cubicle door handle - yuk!)
At one stage I had to take a shower using tea-tree wash when I got home from being out (I was on chemo at the time) and whether or not it helped I don't know but I only had one chest infection during the whole year!