Usually with a positive mantoux test, induration or hardness will occur at the injection site. Some people will have redness at the site...likely due to a mild allergic reaction with the solution of an inflamation due to having the solution injected in the skin. You can have 2 tests done. Often, this is refered to a 2-step mantoux test. It really won't hurt anything. As for exposure, lots of people will test positive in this test....it does not mean that they have active TB, it only means that you had an exposure to TB. Given that you work in a hospital...this might be likely. Only a chest x-ray can confirm active TB. Most people's own immune system will look after the TB if you're healthy...the odds that you are putting your family at risk is very low.... I certainly appreciate your concerns. If you have a second reading that YOU are not content with, I would request a chest x-ray...just to put your mind at rest....if anything....
I tested PPD positive about six years ago, with a very large induration that was exquisitely painful. My arm swelled up besides having the induration. I know that induration is read differently in different populations. Here is a website that has information on interpretation of PPD's:
Because this was work related (I work in a microbiology laboratory), I had a chest xray, which was negative, and insisted on seeing an infectious disease doc. Since my xray was negative, she put me on six months of daily INH, along with B vitamins. I also had a couple of blood tests to check liver function.
I had had negatives for years, and, believe me, I knew this was going to be a positive about 24 hours into it. The reaction was totally different.