1 Although any individual may develop a case of pinworms, the infection occurs most frequently in school children between 5 to 10 years of age.  Pinworm infections occur in all socioeconomic groups; however, human-to-human spread is favored by close, crowded living conditions. Spread among family members is common.
Before they start collecting, stamp collectors try to identify the types of stamps. These will help them segregate and sort stamps according to their classification. On its basic concept, there are three main classifications of stamps â special, commemorative, and definitive.
The tough ones are the letter stamps, issued by the post office when a rate increase was coming, but they weren't sure how much is was going to be. So, they'd print up a bunch of F stamps, for example, for the new first-class rate.