I'd rather worry about man-made contamination than natural contamination. Most food these days is so devoid of any natural ingredients and so highly processed that it's very unlikely you could catch anything from touching it. Swallowing the food on the other hand could be a danger. But, considering the alternative of starvation, I guess we just have to live with what we've got.
I work in the health care feild primarily with kids and we notice (at least at the clinics I have worked at)the kids with the parents who are "germ-a-phobes" are the ones who have increased risk of asthma (a very life threatening disease) as well as the more simplier things such as the common cold. The kids who go out and play in the dirt and mud and aren't constantly told to stay clean (and I don't mean for your cousins wedding) have almost no asthma history and are healthier people all around.
On that note you do need to wash your hands after such things as the bathroom and handeling meat but there is no reason to wash your hands 20x while fixing dinner. Do you think restaraunt chefs do? Besides everytime you wash your hands you dry the skin out, water is one of the most drying agents to your skin (externally) when done in large quanties, it evaporates off your skin taking your natural moisture with it, when this happens enough you get microcuts in the skin its-self and you can end up getting skin infections that way (no fun). In surgery becuase they have to scrub thier hands with a very unforgiving soap and brush (it tore my hands apart so i wore 3 paris of gloves to protect my patients and my doctor finally had me use this trick instead) they wash thier hands (after surgery) with a lotion that is anti-bacterial...but I have found that washing your hands with normal everyday lotion leaves your hands softer and your nails dont get brittle and break as much.
As for sneezing into your hands (I think DamonX mentioned that) it is a horrible habit, and no you shouldn't sneeze into the person next to you, turn your head side ways and sneeze into your elbow crease. This way any germ you have are in an area that is almost never touched and you dont use it to touch anything with such as door knobs the backs of chairs (the dirtiest thing in an office building by the way) keyboards etc.
Well thats my 2 cents
Immune systems work by attacking bugs and leaving markers in our system that alerts the body the next time we are attacked so that we deal with the bugs in an effective and quick way......
If we aren't exposed to germs, or allow our bodies to build our immune systems then we set ourselves up for bigger issues later on.
All our anti-biotics, anti-bacterial stuff is great for hospitals when needed and when truly needed at home but we're breeding super bugs now because of these things!!
As a kid if someone at school had chicken pox we all had to go to their house and catch it as soon as we could!! earlier the better was the rule of thumb........ever seen an adult male with mumps??? NOT NICE
we're too afraid of germs........ok so in some cases we should be but come on its crazy now!!
Sensible hygiene is all that is really needed.