you could get a survey done, not sure as to who does this in the US, is it a realator??. They have a machine that they press onto walls that will read a dampness indicator. dampness usually comes with mould. Ask them to specifically check for mould. There are mould growing seasons like all living organisms
Visually look around windows, esp in the bathroom where it gets wet, around the top of walls and bottom of walls, wallpaper will show signs of mould quite easily.If you can smell a musty smell you are smelling mildew, stick your nose into cupboards and behind wardrobes and take a wiff.
Do check out that link I put on above, this info will be in there , somewhere!