Well, you went to the emergency room and did you ask the Drs. there how to test for the presence of mildew? If not, ask your personal physician. If not them, try your local or county Department of Health.
Unfortunately, I'm only aware of testing for mold if you can SEE it; not how to test if you CAN'T see it. IF you can see it, take a few drops of household bleach and drop it on the 'suspected mold'. If after, say 3-5 minutes, it disappears, then it's probably mold. If it doesn't disappear, then it's probably dirt.
2 years ago, we rented a beach house in Delaware for a week that REEKED of a moldy smell. Fortunately, it was in the basement. The cause, apparently, is from the weekly Cleaning People 'shampooing' the carpets! I know that there's a lot of sand and such down the beach but I thought it was over-kill. We told the Realtor but it didn't get us any $$$ back. Well, we didn't go there this year.
I guess what I'm also trying to say is to get one of your friends that can smell it and see if they can possibly pinpoint the source. In our case, the floor was poured concrete; not wood. Hence, the water from the shampooer just 'sat' there and stunk up the basement! In short order, the carpet will rot and need to be replaced. Try my initial suggestions before you subject your friends to the mold. (THey, too, may have a reaction like you.)