They handle money. They touch other peoples' hands. They clean up bottoms. They touch all kinds of door knobs. And then they pick up food to eat.
Cysts are the 'eggs' made by parasites.
Cysts are so tough not even bleach kills them. They hide under our fingernails when we wash our hands. Then we eat them along with our food. This is called the oral-fecal route. They hatch in the stomach and go to the intestine to live.