While everyone's paying attention to lettuce and "explosive diarrhea" this summer, there's a different illness making the rounds in the U.S. and one of the hardest hit states so far is Illinois. Getty Images Getty ImagesIt's a fungus that spreads in healthcare settings and people who are already sick can be more susceptible to it. And the challenge: the fungus has proven resistant to at least one type of antifungal infection, which makes it really hard to treat. Five Ways to Boost Your Immune System as We Head Into Flu Season We're officially in cold and flu season now. Here are five tips from doctors on how to boost your immune system in the lead-up to the holidays, and beyond.