What is the definition of Established Infection?

An 'established infection' is like a persistent bad habit that you've managed to get your hands on, but now it's starting to show its age. Imagine this: "That sneaky cold from last year? It's an established infection, now it's trying to convince me I've developed a new one, even though the flu shot was a total fluke." There you have it - a classic case of an old infection refusing to let go, even in the most unexpected places.