Everyone in a community is connected to everyone else. People in your circle of friends have different friends who are connected to different friends, and so on. It is often said that almost everyone in the global community is connected to each other by, at most, six people-known as the "six degrees of separation" theory. Of course, identifying which five people might connect you to a villager in Eastern Europe or a city dweller in New Zealand may be difficult, but it is generally possible. In a smaller community, such as a town or city, the connections are easier to trace.
Many diseases that once sickened or killed many people, such as whooping cough, are under control, mostly due to immunizations and better hygiene. Unfortunately, an increasing number of parents are refusing to have their children vaccinated. As a result, fewer members of the community are protected from disease.