Boys used to say this jokingly when I was a kid. Now, after living in a city and depending on public transportation I believe it's pretty safe to say "My hands are weapons of mass destruction".
I had two terrible colds during November, one of which I am sure I got by touching a surface in the Metro.
Think about it. A kid catches a cold at school. He comes home with a runny nose. His mom takes care of him and wipes his nose one last time before sending him back into the school. She hurries to her transit.... She takes a tram for 6 stops and she has to grab hold of multiple handles in getting on, during the jerky ride, and getting off. Then she rushes down to the Metro, where she touches stair rails, the ticket reader, the turnstile, the escalator rail, and handholds inside the car. When she gets to work she passes her badge over the card reader. At every touch she's left germs from her kid's cold.
And how many hundreds or thousands of people are grabbing those same handholds, stair rails, turnstiles in a day, waking up to chills and runny noses the next day?
Then when it becomes cold enough outside that you must wear gloves all the time -- thus offering some manner of protection -- in order to blow your nose you take those gloves off and use the tissue until it's falling apart... with those fingers that touched the change handed to you from your morning caffe' bar. (Change from the money you handed to that unsuspecting barrista with your germy hands!)
It's exponential! And totally mind-boggling for a germophobe like me.
Therefore, I'm currently slathering my hands with germ protection gel, sneezing into my elbow, wiping my laptop and phone with germ killer, holding my breath around people who are obviously sick... and never, ever, ever touching my face with my weapons of mass destruction.