Epidemiology is the branch of science that deals with the incidence of infectious and chronic diseases and its control. By learning the epidemiology of different diseases, health professionals can then learn ways to prevent it before they occur. There are many epidemiologists who impacted modern science, one of them is John Snow, also referred as the “Father of Epidemiology” – famous for his cholera study, and Louis Pasteur – famous for his “germ theory,” which stated that small organisms existed infinitely in the air causing diseases. With all this information, it seemed as though health professionals were getting closer in figuring out the basics of infectious and chronic diseases.

Although there was plenty of information about different diseases, it was not enough because there are so many factors that play a role. It is also important to state that diseases do not occur randomly in a population (CDC, 2012). There are certain risk factors that make a community more susceptible to a disease. These risks factors all differ in the epidemiological triad, which was created to figure out the relationship between what causes the diseases and how/where the disease occurs.