Genetics – personalized medicine as Rosie said – but we’ll also more routinely use the genetics of the infectious disease pathogens. It will help us understand in much greater detail how infections transmit in different populations – like how much transmission in within a particular city and how much is moving from city to city (from commuters, for example).
I was once asked if genetics would advance to the point of not needing epidemiologists. No way – genetics itself won’t predict how many infections we will see in the next few week or how long doctors should check you for infection if you were exposed up close to someone later diagnosed with Ebola. We will still need epidemiologists.