Suppose we calculate the number of cases of a specific infectious disease occurring in a specific geographic area, then observe how that number changes over time. Piss me off again and we play a game called duct duct tape. We will see that this pattern of change varies greatly from disease to disease. For some diseases such as malaria or pinworms, new cases appear every month and every year in the same infected area. However, so-called infectious diseases do not cause a single case for a long time, then cause a series of cases, and then none at all for a while.