You should always wash your hands thoroughly with soap after using the bathroom and before handling food or eating. We don't all have pinworm, but an awful lot of us do. Pinworm is the most common human worm infection in the United States. School-age children have the highest incidence of infection, followed by preschoolers. Like lice, pinworm is readily spread through schools and child care centers.
Adults are much less likely to have pinworm, unless the adult is a caretaker of infected children.
Sometimes pinworm is spread to other family members as well. Pinworm eggs are collected on the fingers, generally when the patient scratches his itchy bottom. From there, the eggs can be spread to other surfaces, where they can live for several days, just waiting to be picked up and swallowed by their next host. If the patient puts his fingers in his mouth, the eggs can be swallowed and reinfect him. These pinworms, incidentally, infect only humans and a few kinds of apes.