Epidemiology’s main role is preventing the onset and spread of disease by finding causes—the reasons why some groups of people are healthier than others—then removing or controlling these causes. Sometimes epidemiologists are called “disease investigators.” Epidemiology is the foundation of public health research. It studies chronic diseases (e.g. heart disease, cancer, and diabetes), infectious diseases (e.g. flu and HIV), outbreaks (e.g. salmonella poisonings), illness from exposure to something in the environment, illness related to people’s genes, injuries and much more.
To find out more about epidemiology, visit the public health tutorial and the CDC's page on epidemiology. You can also take the course Principles of Epidemiology (HLTH 345) for a more in-depth look into the field of epidemiology.