I just bought a house and found out the cats (at least 5) have been living in the crawl space, I didn't notice the smell until the weather starting to get warmer, but my entire house smell of cat urine!! I don't know how to find out if this has an effect on our health or how to get rid of the smell, the cats are using the crawl space as a large litter box, I have already caught two cats and continue to put the traps out but can't close the crawl space door until I know the cats are gone. I wouldn't even know if any have died under there. Help?

You can buy Odo ban http://cleancontrol.com/ or something made specifically from a pet store to clean the smell out and put a door on the crawl space after you clean it out.
You might want to pay somebody that would be willing to take care of cleaning it out for you.
Once it is clean it should be okay.

Any warm blooded stray animal can be a health risk.