We had a great speaker at LIRA this past year and she spoke about things you can "catch" from your fish tank.
Interestingly, she said, that there are some conditions of allergic reactions, that actually grow with more of your things like hands going into the tank. If I remember correctly, some worms ( maybe bristle worm bites), not sure... actually get worse the more you are stung. Opposite of what you would think...
Again, not sure if I got the specifics, right, but basically concept is more times in tank, then over the years, some things get more reaction from the body...