I came across this from a study into the hygiene issues surrounding intinction (dipping the Body of Christ into the chalice as opposed to sipping from a shared cup):
“The findings revealed that bacteria are indeed transferred into the wine when a person’s fingertips are submerged, and these same microbes can then be absorbed onto the wafer of a subsequent participant, in a sponge-like fashion. Not surprisingly, some individuals in the study had small amounts of fecal and other potentially dangerous bacteria on their fingertips, and some of these were recovered from the chalice samplings.”
Another issue raised is that if you have people who are coeliac they may become ill from drinking wine that others have intincted in, because crumbs will have been dropped into the chalice.
It would appear that lips have far less germs on them than fingers. So kissing is better than shaking hands. That should make the Peace more interesting!