Infection can cause an itis, but not all itis is due to infection. Such as inflammatory arthritis (noninfectious) vs septic arthritis (infectious).
senioritis?
I've definitely seen high school seniors get a big head!
In french we occasionally portmanteau -itis (often qualified with "acute" or "mild"), for a comedic yet genuinely emphatic effect. e.g: acute dumbitis/boreditis/tireditis