To expand on a previous comment: "contamination" is relative. NOTHING we eat is sterile in a microbiological sense; the key is to keep things reasonably clean. Our immune system is designed to handle small quantities of bacteria (and many viruses), and such exposure is probably beneficial and necessary, particularly in childhood; illness occurs when the dose gets too high. People with weakened immune systems - AIDS, some cancer patients on chemo, transplant patients on immunosuppression - have a lower threshold for illness, and may need to be more careful; healthy folk can afford to be a bit more casual.
It also depends on where you are. The countertops in hospitals - the surfaces on which people normally lean, and rest their food - are home to more and worse bacteria than the sidewalks outside, because the widespread (and often necessary) use of antibiotics in hospitals has made many of those bacteria resistant to the usual drugs, and of course because hospitals are where you find the people with the worst infections. You might actually do better eating something off the sidewalk than off of the table in the staff lounge! (Again, dosage is the key: in reality, you're generally safe if you ingest a few microbes.)
Finally, people are their own little ecosystems; the average person is home to about a thousand species of bacteria! (A disturbing thought, perhaps, but the vast majority are beneficial or harmless.) If you drop something on the floor of your own house, the bacteria with which it will come into contact are mostly the ones you already harbor; it's generally exposure to NEW microbes which makes people sick.
To expand on a previous comment: "contamination" is relative. NOTHING we eat is sterile in a microbiological sense; the key is to keep things reasonably clean. Our immune system is designed to handle small quantities of bacteria (and many viruses), and such exposure is probably beneficial and necessary, particularly in childhood; illness occurs when the dose gets too high. People with weakened immune systems - AIDS, some cancer patients on chemo, transplant patients on immunosuppression - have a lower threshold for illness, and may need to be more careful; healthy folk can afford to be a bit more casual.
It also depends on where you are. The countertops in hospitals - the surfaces on which people normally lean, and rest their food - are home to more and worse bacteria than the sidewalks outside, because the widespread (and often necessary) use of antibiotics in hospitals has made many of those bacteria resistant to the usual drugs, and of course because hospitals are where you find the people with the worst infections. You might actually do better eating something off the sidewalk than off of the table in the staff lounge! (Again, dosage is the key: in reality, you're generally safe if you ingest a few microbes.)
Finally, people are their own little ecosystems; the average person is home to about a thousand species of bacteria! (A disturbing thought, perhaps, but the vast majority are beneficial or harmless.) If you drop something on the floor of your own house, the bacteria with which it will come into contact are mostly the ones you already harbor; it's generally exposure to NEW microbes which makes people sick.