Suggested fix (unconfirmed): Load a save from before you got infected. If you don't have one, continue playing, as it acts as flavor text with no major inconveniences on normal difficulty.
The problem
I keep getting turned into a mushroom during a fight. How do i get rid of this?
Suggested fix (from YouTube, unconfirmed): You can reroll your characters during the party creation process by repeatedly clicking on the hero or navigating back and forth through the stats screen to randomize the stat generation.