The study of how infectious diseases spread, occur, and are controlled. John Snow (not to be confused with the character Jon Snow of “Game of Thrones” fame) is considered the founder of modern epidemiology. He famously traced a 19th-century cholera epidemic to a contaminated water pump and the pump handle. He chlorinated the water and removed the pump handle, and the disease ended. Today, sometimes epidemiologists talk about tracing modern diseases back to the metaphorical “Pump Handle.”