I have been quiet successful after I saw a BBC program in which they showed with some kind of ultra violet light the way the thing spreads from (especially) toddlers in a kinder garden.
A kid has a runny nose, a cold is coming soon full on for him/her, he or she sneezes on their hands or in the air but touch their faces which have "cold stuff" then touch some toys, other kids, hug the teacher or the teacher touches their hands or toys they touched, then she turns light off, the "stuff" passing onto everything she touches and so on with everyone else...they showed with a green highlighting how from one person to another, one person into objects, the "stuff" gets spread around.....
that wouldn't be enough for the next person who touches to get it....
what they say is that, after we did touch, if we touch our eyes or any point of possible entry to our own bodies, that will do it....
I try to keep away from Sarita when she has a cold, but I keep washing my hands and try reminding my self not to touch my eyes, nose or mouth..... that mostly works.
I used to take vitamin C powder , 1 tea spoon in half a glass of water, dissolved, and that kept me at bay for years as prevention!